Patent Grant
7991918
One or more aspects of the invention generally relate to Transmission Control Protocol (TCP) processing, and more particularly to optimization of TCP-based communications.
Conventional TCP processing is exemplified by systems and methods developed to accelerate data transfer between a client and a server. Software implementations executed on a host processor, e.g., Central Processing Unit (CPU), are typically inexpensive but slow compared with faster but much more expensive dedicated hardware implementations designed to completely offload TCP processing from the host processor.
NIC 150 may share PCI bus 182 with one or more other PCI Devices 180. NIC 150 includes a PCI Interface 175, a Dedicated Processor 155, a Medium Access Controller (MAC) 165, a Dedicated Memory 160, and an ETHERNET Interface 170 to interface to an ETHERNET Network 172. Software Driver 119 for NIC 150 communicates between NIC 150 and Application Program 117 executing on CPU 110. An Application Memory Space 125, a TCP Stack Memory Space 145, and a Driver Memory Space 135 are allocated within System Memory 130.
Dedicated Processor 155 within NIC 150 is used for TCP processing in lieu of having CPU 110 execute TCP Stack 115 to perform TCP processing. Therefore NIC 150 offloads CPU 110, freeing CPU 110 processing cycles for other applications. Likewise, Dedicated Memory 160 replaces TCP Stack Memory Space 145, freeing TCP Stack Memory Space 145 for allocation to other applications. However, NIC 150, including Dedicated Memory 160 and Dedicated Processor 155, is more costly than a software implementation for TCP processing executed on CPU 110.
Therefore, there is a need for a partial hardware implementation that optimizes TCP processing by offloading some tasks from a host processor and is less costly than a hardware implementation including a dedicated processor.
Various embodiments of a method of the invention include writing a command including an index corresponding to a delegated connection to an entry in a command ring, reading the command from the entry in the command ring, executing the command, and writing command specific status to the entry in the command ring.
Various embodiments of a method of the invention include writing a notification descriptor to an entry in a notification ring, reading the notification descriptor from the entry in the notification ring, and determining connection information for a delegated connection based on the notification descriptor.
Various embodiments of the invention include a command ring and a command unit. The command ring is configured to receive commands written by a TCP stack. The command unit is configured to read commands from the command ring and to process the commands.
Various embodiments of the invention include a notification unit within an offload unit and a notification ring. The offload unit is configured to write notification descriptors to the notification ring. The notification ring is configured to output notification descriptors read by a TCP stack.
The current invention involves new systems and methods for transmitting commands and connection information between an offload unit and a TCP stack executing in the main host processor.
Accompanying drawing(s) show exemplary embodiment(s) in accordance with one or more aspects of the present invention; however, the accompanying drawing(s) should not be taken to limit the present invention to the embodiment(s) shown, but are for explanation and understanding only.
In the following description, numerous specific details are set forth to provide a more thorough understanding of the present invention. However, it will be apparent to one of skill in the art that the present invention may be practiced without one or more of these specific details. In other instances, well-known features have not been described in order to avoid obscuring the present invention.
I/O Controller 240 includes a controller for PCI Bus 282 and may include controllers for System Management Bus (SMBus) 142, Universal Serial Bus (USB) 144, and the like. In an alternative embodiment, I/O Controller includes a controller for PCI Express bus. I/O Controller 240 also includes HOT Unit 250, effectively decoupling HOT Unit 250 from devices coupled to I/O Controller 240 via PCI Bus 282. Specifically, Hub-to-hub Interface 126 may be a high speed industry standard or proprietary bus coupling HOT Unit 250 to System Memory 130 via System Controller 120. Devices coupled to I/O Controller 240 share the bandwidth available on PCI Bus 282 which is typically lower than the bandwidth available on Hub-to-hub Interface 126. The location of HOT Unit 250 within I/O Controller 240 results in lower latency between HOT Unit 250 and both CPU 110 and System Memory 130 compared with latency between NIC 150 and CPU 110 shown in
HOT Unit 250 includes a controller interfacing to Input/Output Interface 242. Input/Output Interface 242 may couple HOT Unit 250 to a physical layer (PHY), e.g., 802.3 PHY, HPNA 1.0 PHY, HPNA 2.0 PHY, or the like. In an alternate embodiment a PHY is included within HOT Unit 250 and Input/Output Interface 242 is an ETHERNET interface such as Gigabit ETHERNET. I/O Controller 240 may be a single integrated circuit or single semiconductor platform.
TCP Stack 215 selects one or more TCP connections as delegated connections. A delegated connection is a TCP connection processed by HOT Unit 250 with minimal intervention by TCP Stack 215. Connections that are not delegated or delegated connections that require special processing are processed entirely or partially by TCP Stack 215. TCP Stack 215 sets up a delegated connection by initializing an entry in a delegated connection table, as described further herein, within HOT Unit 250 using Driver 255 stored within System Memory 130. Driver 255 is effectively a translator between TCP Stack 215 and HOT Unit 250, issuing commands to HOT Unit 250 as requested by TCP Stack 215. Driver 255 also informs TCP Stack 215 when notifications are received from HOT Unit 250. Although communications between TCP Stack 215 and HOT Unit 250 are accomplished using Driver 255, Driver 255 may not be explicitly indicated henceforth.
Unlike the delegated connection table which only stores connection state data for delegated connections, Connection Table 245 within System Memory 130 stores connection state data for all active connections. Therefore, TCP Stack 215 may assume processing of any delegated connection as requested by HOT Unit 250. Processing a delegated connection by TCP Stack 215 is referred to as “legacy processing.”
A Transmit Engine 320 includes subunits configured to parse and edit outbound frames, including acknowledgement insertion, and checksum cyclic redundancy check computation, producing outbound frames. A Transmit Interface 330 includes one or more buffers to store outbound frames for transmission and subunits configured to interface with a PHY coupled to HOT Unit 250 via Input/Output Interface 242. In an alternate embodiment of HOT Unit 250, the PHY is integrated into HOT Unit 250. Transmit Engine 320 is coupled to a Delegated Connection Table (DCT) 350, which stores connection state data for delegated connections. Delegated Connection Table 350 is a storage resource, e.g. random access memory (RAM), a register file, or the like. At least a portion of the connection state data for delegated connections is also stored in Connection Table 245.
State information stored in Delegated Connection Table 350 may include an acknowledgement state, connection addresses, pointers to system memory buffers, connection tracking flags, event control information, transmit window size, receive window size, timestamp data, and the like. The acknowledgement state may include a sequence number of the next expected sequence number to be received, thresholds controlling the timely generation of acknowledgements, and the like. Transmit Engine 320 reads and writes portions of Delegated Connection Table 350 during frame processing using a connection table index, DCT index, to access an entry associated with a delegated connection. Connection state data stored in the entry is updated by TCP Stack 215, Transmit Engine 320, and Receive Engine 360 while the delegated connection is active, as described in relation to
Receive Interface 370 includes a subunit configured to interface with the PHY coupled to HOT Unit 250 via Input/Output Interface 242. Receive Interface 370 also includes a receive FIFO (first-in first-out) buffer for storing received frames that are destined for Receive Engine 360. Receive Engine 360 uploads either a partially processed frame or just the TCP payload data to System Memory 130 via DMA Engine 310, as described further herein.
Receive Engine 360 includes subunits configured to parse the incoming frame and determine whether or not the frame is valid, i.e., computing checksums, verifying flags, and identifying the frame type, e.g., IP, UDP, TCP, and the like. When a parsed frame is not valid it is uploaded to a legacy buffer in Driver Memory Space 235 for legacy processing. If the received frame contains an IP packet with a TCP segment, the TCP Stack 215 is notified and copies the uploaded frame from the legacy buffer to Application Memory Space 227 after performing the required TCP processing.
When a parsed frame is determined to be valid, Receive Engine 360 extracts the source IP address, TCP sequence number (SN), TCP acknowledgement (ACK) number, TCP source and destination port numbers, the TCP window size, the TCP header length, and the like. Parsed frames received on non-delegated connections are uploaded to legacy buffers in Driver Memory Space 235 for processing. A parsed frame that is received on a delegated connection and that is not a special case, e.g., out-of-order sequence numbers, TCP Push flag set, and the like, is processed and the TCP payload data is uploaded to a user buffer in Application Memory Space 227. Uploading TCP payload data directly to Application Memory Space 227 is more efficient than uploading payload data through Driver Memory Space 235 since the TCP payload data does not need to be subsequently copied from Driver Memory Space 235 to Application Memory Space 227.
If, in step 412 TCP Stack 215 determines the connection should not be delegated for processing by HOT Unit 250, then in step 414 TCP Stack 215 sets up an entry in CT 245 for processing the connection and proceeds to step 422. If, in step 412 TCP Stack 215 determines the connection should be delegated for processing by HOT Unit 250, then in step 416 TCP Stack 215 issues a command to HOT Unit 250 setting up an entry in DCT 350 with connection state data. In step 418 TCP Stack 215 determines whether or not to issue a post receive buffers (PRB) command to HOT Unit 250, as further described herein, providing HOT Unit 250 with locations and sizes, in System Memory 130, of one or more user buffers. If, in step 418 TCP Stack 215 determines a PRB command will be issued, then in step 420 TCP Stack 215 issues a PRB command. If, in step 418 TCP Stack 215 determines a PRB command will not be issued, then TCP Stack 215 proceeds to step 422. In step 422 connection setup is complete.
If, in step 425 HOT Unit 250 determines the frame was received on a delegated connection, then in step 426 HOT Unit 250 completes parsing of the frame, extracting the TCP payload data. In step 427 HOT Unit 250 determines if a user buffer is available, and, if so, then in step 428 HOT Unit 250 uploads the TCP payload data to one or more user buffers. If, in step 427 HOT Unit 250 determines a user buffer is not available, then in step 430 HOT Unit 250 uploads a portion of the payload data to a legacy buffer and notifies TCP Stack 215. In one embodiment the portion is specified by a “startup limit” value stored in the entry in the DCT 350 corresponding to the delegated connection. The “startup limit” is a variable that may take a maximum value equal to the maximum receive frame size and a minimum value as determined by Application Program 217 or TCP Stack 215.
In step 432 TCP Stack 215 processes the portion of the TCP payload data uploaded to the legacy buffer. In step 434 HOT Unit 250 determines if one or more PRB commands issued by TCP Stack 215 for the delegated connection have been processed. In step 436 HOT Unit 350 uploads the remaining TCP payload data to one or more user buffers. If, in step 434 HOT Unit 250 determines one or more PRB commands for the delegated connection have not been processed, then in step 438 HOT Unit 250 uploads the remaining TCP payload data to a legacy buffer and notifies TCP Stack 215. In an alternate embodiment, TCP Stack 215 completes step 434 and in step 438 TCP Stack 215 instructs HOT Unit 250 to upload any remaining TCP payload data to a legacy buffer.
In one embodiment, message signaled interrupts (MSIs) provide a mechanism for HOT Unit 250 to use multiple interrupt vectors to signal its various interrupt sources. Utilizing MSIs enables efficiencies in interrupt handling of the host. In one embodiment, Computing System 200 uses up to eight interrupt vectors.
In step 452 Application program 217 sets cwnd to 1 segment for the delegated connection and TCP Stack 215 outputs a transmit buffer descriptor to HOT Unit 250, as described further herein in relation to
In step 456 TCP Stack 215 determines if cwnd is greater than or equal to ssthresh for the delegated connection, and if so, then in step 458 TCP Stack 215 exponentially increases, i.e., opens, the cwnd based on the number of ACKs received for the delegated connection. In step 458 TCP Stack 215 also outputs a transmit buffer descriptor to HOT Unit 250 and returns to step 454.
In one embodiment in step 458 TCP Stack 215 configures HOT Unit 250 to notify TCP Stack 215 for each received ACK. In an alternate embodiment TCP Stack 215 configures HOT Unit 250 to notify TCP Stack 215 for a count of received ACKs, thereby performing some ACK coalescing. If, in step 456 TCP Stack 215 determines ssthresh is less than cwnd for the delegated connection, then in step 460 TCP Stack 215 is in congestion avoidance phase. When congestion avoidance is used cwnd opens linearly, until either cwnd equals the maximum transmit window size or packets are dropped.
In a further alternate embodiment a user buffer descriptor may include any combination of a user buffer address, a user buffer length, and a user buffer end address. As previously mentioned, user buffer descriptors are provided to HOT Unit 250 by TCP Stack 215 using a PRB command. Providing physical memory addresses located in Application Memory Space 227 to HOT Unit 250 enables HOT Unit 250 to upload payload data directly to Application Memory Space 227.
Application Program 217 manages user address space which is a virtually contiguous address space allocated by an operating system. When Application Program 217 transfers the user address space information to TCP Stack 215, TCP Stack 215 requests that the operating system lock the memory corresponding to the user buffer address space. The operating system locks the amount of memory and returns one or more physical addresses (and lengths) corresponding to physically contiguous portions of System Memory 130 to TCP Stack 215. The physical address space, accessed by HOT Unit 250, is managed by TCP Stack 215 and is not necessarily physically contiguous. TCP Stack 215 translates between the user address space and the physical address space. In an alternate embodiment Driver 255 translates between the user address space and physical address space.
Communication between Driver 255 and HOT Unit 250 is accomplished through data structures stored in Driver Memory Space 235. A ring is a data structure that includes several entries, as described further herein. A ring is organized as a circular queue of the entries with a pointer used by Driver 255 and another pointer used by HOT Unit 250. Each ring is stored in contiguous physical memory in Driver Memory Space 235.
In addition to the “own” bit, each Command Ring Entry 603 includes a command field, a DCT index, command-specific control and/or status information, command-specific data, and the like. As was previously mentioned, the DCT index identifies an entry in DCT 350 corresponding to a delegated connection. The command field includes a command identifier for a command such as, a PRB command, an update table entry (UTE) command, an invalidate table entry (ITE) command, a dump connection buffer table entry (DCBTE) command, and the like. When a command is written by Driver 255 the command specific control/status information includes command specific control. When a command is read and updated by HOT Unit 350, the command specific control/status information is updated to include command specific status. The command specific data is written by Driver 255 and read by HOT Unit 350, as described further herein.
The PRB command is used by Application Program 217 to pass user buffer descriptors to HOT Unit 350, via TCP Stack 215 and Driver 255. Each user buffer descriptor indicates a physical address in Application Memory Space 227 for HOT Unit 350 to upload payload data to. TCP Stack receives one or more user addresses and determines corresponding physical addresses for inclusion in a user buffer descriptor. TCP Stack 215 can post one or more user buffer descriptors via Driver 255 using a PRB command, on behalf of Application Program 217, for a single delegated connection table entry. Driver 255 includes the number of user buffers in the command-specific control and/or status information field within a PRB command. Because Driver 255 does not have the information necessary to determine how many of the previously posted user buffers have been uploaded to by HOT Unit 350, HOT Unit 350 writes a value in the command-specific control and/or status information field indicating the number of user buffers accepted from the PRB command.
The command-specific control and/or status information field in a PRB command also includes a “sync” bit. TCP Stack 215 requests Driver 255 to write the “sync” bit when a notification command including an asserted legacy flag, as described further herein in relation to
The command-specific data field in a PRB command constructed by Driver 255 includes a starting TCP sequence number corresponding to the first byte of the first buffer posted in the PRB command, a user buffer descriptor for each user buffer included in the PRB command, and the like. A user buffer descriptor includes a physical address specifying a location in Application Memory Space 227, the length of the user buffer, descriptor flags indicating any special handling, and the like.
The UTE command is used by Driver 255 to update an entry in DCT 350 and is used to setup a delegated connection and update connection data while a delegated connection is active. The ITE command is used to invalidate a delegated connection. When HOT Unit 250 receives an ITE command it waits, if necessary, for processing by Transmit Engine 320 and Receive Engine 360 to complete (while blocking any new TCP processing from starting) before clearing the delegated connection corresponding to the DCT index specified in the ITE command. The DCBTE command causes HOT Unit 350 to upload a portion of an entry specified by the DCT index included in the DCBTE command to a legacy buffer.
Driver 255 can access Command Ring 601 without interfering with transmit or receive processing for the PRB command. This permits Driver 255 to provide HOT Unit 350 with new user buffers in a timely manner, improving the likelihood that receive frames can be accepted by HOT Unit 350 rather than blocked.
Notification Ring 611 includes several entries, each entry shown in
In addition to the “own” bit, each Notification Ring Entry 613 includes a notification flags field, a DCT index, an optional tag that, if present, provides a reference to a particular legacy buffer, the next expected sequence number, the highest received ACK number, the most recently received transmit window size, current TCP timestamp, and the like, for the delegated connection specified by the DCT index. The notification flags field includes a “legacy” flag, a “push notification” flag, a “duplicate ACK” flag, a “sequence number threshold” flag, an “ACK threshold” flag, a “request buffer” flag, and the like. The “legacy” flag is asserted when payload data or partially parsed frame data has been uploaded by HOT Unit 250 to a legacy buffer. The function of the “push notification” flag, the “duplicate ACK” flag, the “sequence number threshold” flag, the “ACK threshold” flag, and the “request buffer” flag are described in relation to
The optional tag is included when HOT Unit 250 uploads payload data or partially parsed frame data to a legacy buffer, as described further herein in relation to
HOT Unit 250 can use Notification Ring 611 to inform Driver 255 in a timely manner of connection conditions requiring further processing by Driver 255 with minimal impact, if any, on transmit or receive processing by HOT Unit 250. The operation of the Notification Ring 611 permits Driver 255 to provide HOT Unit 350 with new user buffers in a timely manner, improving the likelihood that received frames can be accepted by HOT Unit 350 rather than blocked.
Receive Descriptor Ring 621 includes several entries, each entry shown in
In addition to the “own” bit, each Receive Descriptor Ring Entry 623 includes a legacy buffer descriptor, a receive control and/or status field, and the like. As previously described in relation to
When a Receive Descriptor Ring Entry 623 is written by Driver 255 the Receive Descriptor Ring Entry 623 can include, among other bits, a bit requesting that HOT Unit 350 issue an interrupt when data is uploaded to the legacy buffer specified in the Receive Descriptor Ring Entry 623. When a Receive Descriptor Ring Entry 623 is read and updated by HOT Unit 350, the receive control and/or status information is updated to include connection status when payload data or parsed frame data is uploaded to a legacy buffer. The receive control and/or status information written by HOT Unit 350 for a non-delegated connection upload to a legacy buffer can include an end of receive frame indicator, exceeded maximum frame size indicator, and the like. The receive control and/or status information written by HOT Unit 350 for a delegated connection upload to a legacy buffer can include startup buffer indicator, user buffer not available indicator, end of receive frame, out-of-range ACK received indicator, and the like.
Transmit Descriptor Ring 631 includes several entries, each entry shown in
In addition to the “own” bit, each Transmit Descriptor Ring Entry 633 includes a transmit buffer descriptor, DCT index, transmit-specific control, a transmit control/status field, a transmit buffer byte count, and the like. A transmit buffer descriptor includes a physical address specifying a location in Application Memory Space 227 or TCP Stack Memory Space 225 where frame data for transmission is stored. HOT Unit 250 reads the frame data for transmission from Driver Memory Space 235 using the physical address. The transmit-specific control can include a request for Transmit Engine 320 to save the sequence number of the first byte of a frame in DCT 350. When an ACK is received for the frame, HOT Unit 250 may generate a notification command.
The transmit control and/or status field written by Driver 255 can include an end of transmit frame indicator, a bit enabling TCP segmentation, one or more bits enabling TCP checksum computation in HOT Unit 250, a maximum segment size for use during TCP segmentation, and the like. When a Transmit Descriptor Ring Entry 633 is read and updated by HOT Unit 250, the transmit-specific control and/or status information is updated to include transmit-specific status. Transmit-specific status can include a loss of carrier indicator, a transmit retry count, a retry error, and the like.
An entry in CDT 720 is initialized by CMD Unit 710 when a delegated connection is set up. An entry within CDT 720 includes delegated connection state information for a delegated connection, such as an expected sequence number, an ACK number, timestamp data, a count of unACKnowledged frames, and the like. Fields within the entry in CDT 720 are read and optionally modified by Transmit Engine 320 when frames are constructed for transmission on the delegated connection. Likewise, fields within the entry in CDT 720 are read and optionally modified by units within Receive Engine 360 as incoming frames on the delegated connection are processed. An entry in CBT 715 is written with one or more user buffer descriptors by CMD Unit 710 when a PRB command is received for a delegated connection. The user buffer information is read and optionally modified by a Buffer Upload Unit 745 within Receive Engine 360.
The delegated connection information has been distributed between CBT 715, CDT 720, and CMT 725 in such a manner as to decouple accesses of the state information stored in CDT 720 from user buffer postings effecting CBT 715. Furthermore, because the state information is updated by Receive Engine 360 based on the most recently received frame, Transmit Engine 320 and TCP Stack 215 can access current state information during frame construction. Likewise, because the state information is also updated by Transmit Engine 320 based on the most recently transmitted frame, Receive Engine 360 and TCP Stack 215 can access up-to-date state information during frame processing.
Within Receive Interface 370, a buffer, Receive FIFO 730 buffers incoming frames. Receive Interface 370 outputs frames and valid frame indicators to a Pre-parse Unit 735 within Receive Engine 360. Pre-parse Unit 735 parses valid frames, producing partially parsed frames, and reads CMT 725 to determine whether or not the frame was received on a delegated connection. Pre-parse Unit 735 outputs the partially parsed frames to a Parsing Unit 740. Parsing Unit 740 determines a protocol type for each partially parsed frame, e.g., TCP, UDP, IP, and the like, and optionally parses the partially parsed frames producing parsed frames and partially parsed frames. Parsing Unit 740 reads CDT 720, determines if one or more special cases exist, and outputs the partially parsed frames, parsed frames, or frames, to Buffer Upload Unit 745. Parsing Unit 740 also optionally sets notification flags, described further herein, stored in a storage element, such as a register within Notification Unit 750.
Buffer Upload Unit 745 reads CBT 715 and optionally writes CBT 715 and CDT 720. Buffer Upload Unit 745 uploads the frames, partially parsed frames, and parsed frames to System Memory 130 via DMA Engine 310. Buffer Upload Unit 745 specifies locations to write in System Memory 130 based on data stored in a user buffer descriptor stored in CBT 715 or a legacy buffer descriptor received from Driver 255 via the Receive Descriptor Ring 621. Similarly, Transmit Engine 320 specifies locations to read in System Memory 130 based on transmit buffer descriptors received from Driver 255 via the Transmit Descriptor Ring 631. Notification Unit 750 outputs notifications to Driver 255 via DMA Engine 310 to Notification Ring 611.
Delegated connection information for a limited number of connections is stored in CMT 725, and after the limited number is reached, connection information for excess connections is stored only in CT 245 (in
If, in step 803, Pre-parse Unit 735 determines the valid frame is a TCP frame, then in step 807, Pre-parse Unit 735 reads one or more entries from CMT 725. In step 809 Pre-parse Unit 735 determines if the TCP frame, hereafter referred to as “the frame,” was received on a delegated connection, i.e., if the frame matches an entry in CMT 725. Pre-parse Unit 735 extracts the destination IP address, the source IP address, the source TCP port, and the destination TCP port from the frame and uses these values to search for a matching entry in CMT 725. A match indicates that the connection has been delegated. If, in step 809, Pre-parse Unit 735 determines the frame was not received on a delegated connection, then in step 813, legacy processing of the frame is completed. Pre-parse Unit 735 initiates legacy processing by outputting the frame to Buffer Upload Unit 745 via Parsing Unit 740 and indicating the frame was not received on a delegated connection. Buffer Upload Unit 745 uploads the at least partially parsed frame to Driver Memory Space 235 via DMA Engine 310 and notifies Driver 255 with a request for legacy processing, as described further herein.
If, in step 809, Pre-parse Unit 735 determines that the frame was received on a delegated connection, then in step 811 Pre-parse Unit 735 outputs the partially processed frame to Parsing Unit 740. In step 811 Parsing Unit 740 parses the partially processed frame, producing a parsed frame and determines if there is a special case, e.g., IP or TCP options, invalid flags, or the like, and if so, in step 812 Parsing Unit outputs the parsed frame to Buffer Upload Unit 745 indicating there is a special case. In step 812, Buffer Upload Unit 745 sets a “sync request” flag in an entry in CBT 720 corresponding to the delegated connection and flushes any user buffer descriptors in the entry in CBT 715 corresponding to the delegated connection. In step 813, Buffer Upload Unit 745 uploads the parsed frame to Driver Memory Space 235 via DMA Engine 310 and notifies Driver 255 with a request for legacy processing. Setting the “sync request” flag for a delegated connection in step 812 indicates that the delegated connection is processed using legacy processing. Receive Engine 360 does not accept user buffer descriptor commands for the delegated connection until the sync request flag is cleared by a future buffer posting event, as further described in relation to
If, in step 811 Parsing Unit 740 determines there is not a special case, then in step 815 Parsing Unit 740 reads an entry in CDT 720 corresponding to the delegated connection. In step 817 Parsing Unit 740 and Buffer Upload Unit 745 determine which, if any, notification flags stored in Notification Unit 750 are set, as further described in relation to
If, in step 819, Parsing Unit 740 determines the SN is equal to the DCT SN, then in step 823 Parsing Unit 740 outputs the parsed frame to Buffer Upload Unit 745. In step 823 Buffer Upload Unit 745 reads the entry in CBT 715 corresponding to the delegated connection. In step 825, Buffer Upload Unit 745 determines if a user buffer is available. The term “user buffer” is interchangeable with the term “HOT buffer”. If a HOT buffer is not available, then in step 827 Buffer Upload Unit 745 either waits for a HOT buffer to become available or uploads the parsed TCP frame to a legacy buffer via DMA Engine 310, as further described in relation to
If, in step 825, Buffer Upload Unit 745 determines a HOT buffer is available, then in step 829 Buffer Upload Unit 745 completes processing of the parsed frame and uploads at least a portion of the payload data to the HOT buffer, as further described in relation to
In step 830 Parsing Unit 740 determines if the SN extracted from the frame is less than the DCT SN read from CDT 720 in step 815 of
In step 838 Buffer Upload Unit 745 flushes any HOT buffers corresponding to the delegated connection stored in CBT 715. In step 840, Buffer Upload Unit 745 sets a “sync request” flag corresponding to the delegated connection in CBT 715 and optionally updates connection state data for the delegated connection, e.g., Fast ACK, DCT SN, ACK number, and the like, stored in CDT 720. In step 813, Buffer Upload Unit 745 uploads the parsed TCP frame to Driver Memory Space 235 via DMA Engine 310 and notifies Driver 255 with a request for legacy processing.
In step 850, Buffer Upload Unit 745 determines if a “request buffer” flag is set in the entry, read in step 823 of
In step 854 Buffer Upload Unit 745 uploads a number of bytes, determined by a “startup limit” value to a legacy buffer via DMA Engine 310. The startup limit, initialized by TCP Stack 215 is stored in the entry in CDT 720 corresponding to the delegated connection. In step 856, Buffer Upload Unit 745 sets the “request buffer” flag stored in Notification Unit 750 and Notification Unit 750 issues a notification to Driver 255 via the notification ring. The notification includes the same tag value that was used in the tag field from the associate legacy buffer descriptor. Notification Unit 750 clears the notification flags after sending the notification. Techniques known to those skilled in the art are used to ensure that the parsed frame is uploaded to Driver Memory Space 235 before Driver 255 receives the corresponding notification.
In step 858 Buffer Upload Unit 745 determines if a value indicating the “fullness” of Receive FIFO 730 is greater than a limit, e.g., a “high water” mark, and, if so Buffer Upload Unit 745 proceeds to step 862. In one embodiment, the high water mark is fixed. In an alternate embodiment, the high water mark is stored in a register programmed by Driver 255. If, in step 858, Buffer Upload Unit 745 determines the value indicating the “fullness” of Receive FIFO 730 is not greater than the “high water” mark, then in step 860 Buffer Upload Unit 745 determines if a buffer request timer has expired. If, in step 860, Buffer Upload Unit 745 determines the buffer request timer has expired, then in step 862 Buffer Upload Unit 745 sets the “sync request” flag stored in CBT 715 and the legacy flag stored in Notification Unit 750. In step 813, Buffer Upload Unit 745 uploads the parsed frame to Driver Memory Space 235 via DMA Engine 310. Notification Unit 750 issues a notification to Driver 255 via the notification ring, Notification Unit 750 clears the notification flags, and Receive Engine 360 returns to step 801 in
If, in step 860 Buffer Upload Unit 745 determines the buffer request timer has not expired, in step 864 Buffer Upload Unit 745 determines if a user buffer is available, i.e., if Application Program has posted a user buffer via the command ring. If a user buffer is not available, Buffer Upload Unit 745 returns to step 858. If a user buffer is available, Buffer Upload Unit 745 completes processing of the parsed frame and uploads the payload data to the user buffer in step 829, as further described in relation to
In addition to transmitting ACKs to the sender, Driver 255 is notified as frames are received by HOT Unit 250 based on sequence numbers, timers, and the like. CDT 720 is updated by increasing DCT SN by the received TCP payload size, a count of unACKnowledged frames is incremented, and the most recently received TCP timestamp extracted from the received frame is stored in CDT 720 for the delegated connection, if the TCP timestamp option was appropriately included in the received frame.
In step 876 Parsing Unit 740 determines if the count of unACKnowledged frames is greater than an unACKnowledged frame limit, and if so, proceeds to step 880. The unACKnowledged frame limit is stored in CDT 720 for the connection and is determined by TCP Stack 215. In an alternate embodiment, Parsing Unit 740 determines if the count of unACKnowledged frames received on the delegated connection is greater than or equal to the unACKnowledged frame limit in step 876. In another alternate embodiment, Buffer Upload Unit 745 determines if the count of unACKnowledged frames is greater than the unACKnowledged frame limit.
If, in step 876, Parsing Unit 740 determines the count of unACKnowledged frames is less than or equal to the unACKnowledged frame limit, then Parsing Unit 740 determines if a transmit timer has expired in step 878. A transmit ACK timer is configured to expire before a sender's retransmit timer would expire, in order to minimize unnecessary retransmissions due to the sender not receiving timely ACKs. In one embodiment, the expiration period of the transmit ACK timer is a constant for all delegated connections. In an alternate embodiment, the expiration period of the transmit ACK timer may be programmed by TCP Stack for each delegated connection.
If, in step 878 Parsing Unit 740 determines the transmit ACK timer has expired, then Parsing Unit 740 signals Transmit Engine 320 to generate an ACK for the parsed frame in step 880 and Transmit Engine 320 outputs the parsed frame to Buffer Upload Unit 745. In step 882, Buffer Upload Unit 745 updates the unACKnowledged frame count stored in the entry in CDT 720 for the connection by setting it to zero and updates a “last ACK sent” value to the SN value extracted from the frame. Buffer Upload Unit 745 also updates connection state data such as the incremental ACK number, the incremental sequence number, and the like, and resets the transmit ACK timer before proceeding to step 886.
If, in step 878, Buffer Upload Unit 745 determines the transmit ACK timer has not expired, then Buffer Upload Unit 745 updates the entry corresponding to the delegated connection in CDT 720 in step 884, e.g., by updating the count of unACKnowledged frames, and the like.
In step 886 the payload data are uploaded by Buffer Upload Unit 745 via DMA Engine 310 to a HOT buffer TCP in Application Memory Space 227. In step 888, Notification Unit 750 determines if any notification flags are set, and, if so, in step 890, Notification Unit 750 issues a notification to Driver 255 via the notification ring. Notification Unit 750 constructs an event notification descriptor, including the notification flags, the transmit window size, SN, the last ACK number, the TCP timestamp value, the tag value from the legacy descriptor, and the like. Notification Unit 750 clears the notification flags after sending the notification.
Notification Unit 750 outputs the event notification descriptor to DMA Engine 310 which transfers the event notification descriptor to an offload event notification ring stored in Driver Memory Space 235. The offload event notification ring is organized as a circular queue in a contiguous memory block. HOT Unit 250 writes the offload event notification ring and Driver 255 reads the offload event notification ring. TCP Stack 215 may use data read from the offload event notification ring to update CT 245, thereby maintaining coherence between CT 245 and DCT 350. TCP Stack 215 may also maintain coherence between CT 245 and DCT 350 by uploading entries from CDT 715 to one or more legacy buffers.
Following step 890, Receive Engine 360 returns to step 801 to process another valid frame. If, in step 888, Notification Unit 750 determines that one or more notification flags are not set, then Receive Engine 360 returns to step 801 to process another valid frame.
Reducing the frequency of interrupts CPU 110 received during frame processing frees the CPU 110 to execute other applications, typically improving performance of those applications by increasing the number of application instructions CPU 110 executes. The thresholds permit flexibility in determining a balance between interrupts to notify TCP Stack 215 of receive connection status and transmit connection status, for delegated connections.
In step 901 Parsing Unit 740 determines if the transmit window is shrinking from the right. Parsing Unit 740 determines the transmit window is shrinking from the right when an ACK number extracted from the frame summed with the receive window size extracted from the frame is less than a maximum transmit window size stored in CDT 720 for the delegated connection. Buffer Upload Unit 745 updates the maximum transmit window size stored in CDT 720 for the delegated connection with the transmit window size extracted from the frame. If, in step 901, Parsing Unit 740 determines the transmit window is shrinking from the right, then in step 903, Parsing Unit 740 sets a transmit window notification flag in Notification Unit 750.
In step 905, Parsing Unit 740 determines if duplicate ACKs (same ACK numbers in one or more received frames) have been received, indicating that the destination is requesting retransmission of one or more frames. If, in step 905, Parsing Unit 740 determines duplicate ACKs have been received, then in step 903, Parsing Unit 740 sets a “duplicate ACK notification” flag in Notification Unit 750.
In step 907, Parsing Unit 740 determines if SN is greater than a threshold, e.g., limit, the threshold indicating an incremental sequence number. The incremental sequence number is initialized by TCP Stack 215 when a delegated connection is set up and is updated by Buffer Upload Unit 745 whenever a notification is sent to Driver 255. In one embodiment, the incremental sequence number is updated by increasing the incremental sequence number by a sequence increase value. The sequence increase value may be fixed or programmed by TCP Stack 215. If, in step 907, Parsing Unit 740 determines SN is greater than the threshold, then a sequence number threshold flag is set in step 903.
In step 909, Parsing Unit 740 determines if a last ACK number (the most advanced ACK number received for the delegated connection) stored in CDT 720 is greater than a limit, the limit indicating an incremental ACK number. The last ACK number is initialized by TCP Stack 215 when a delegated connection is set up and is updated by Buffer Upload Unit 745 whenever an ACK is received. The incremental ACK number is initialized by TCP Stack 215 when a delegated connection is set up and is updated by Buffer Upload Unit 745 whenever a notification is sent to TCP Stack 215. In one embodiment, the incremental ACK number is updated by increasing the incremental ACK number by an ACK increase value. The ACK increase value may be fixed or programmed by TCP Stack 215.
In step 909, Parsing Unit 740 may also determine if the last ACK number stored in CDT 720 is greater than another limit, the other limit indicating a specific ACK number programmed by TCP Stack 215. If, in step 909, Parsing Unit 740 determines the last ACK number is greater than the limit (indicating an incremental ACK number) or the other limit (indicating a specific ACK number), then an ACK threshold flag is set in step 903.
In step 911, Parsing Unit 740 determines if one or more timers have expired. A receive ACK timer is configured to expire before TCP Stack's 215 retransmit timer expires in order to minimize unnecessary retransmissions. The expiration period of the receive ACK timer for a delegated connection stored in a register may be programmed by TCP Stack 215 and may be based on a round trip time for the delegated connection. A receive SN timer is configured to notify TCP Stack 215 that data has been received by HOT Unit 250. The expiration period of the receive SN timer for a delegated connection stored in a register may be programmed by TCP Stack 215. In an alternate embodiment, the expiration periods of the receive ACK timer and the receive SN timer are stored in an entry in CMT 725 corresponding to a delegated connection.
If, in step 911, Parsing Unit 740 determines that a timer has expired, then a corresponding notification flag is updated in step 903 and Parsing Unit 740 proceeds to step 913. For example, when the receive SN timer expires, the “sequence number threshold” flag is set and when the receive ACK timer expires, the “ACK threshold” flag is set. If, in step 911, Receive Engine 360 determines none of the one or more timers has expired, then Parsing Unit 740 outputs the parsed frame to Buffer Upload Unit 745 in step 913 and Buffer Upload Unit 745 determines if the push flag extracted from the frame has been asserted. If the push flag was asserted, then a push notification flag is set in step 903 and Buffer Upload Unit 745 proceeds to step 819 of
Until the retransmitted frame is received, Buffer Upload Unit 745 uploads frames received for the connection to legacy buffers. TCP Stack 215 copies the payload data from legacy buffers to user buffers. When the retransmitted frame is uploaded to a legacy buffer, TCP Stack 215 sends an ACK for all frames received in sequence. Transmit Engine 320 updates the DCT SN stored in CDT 720 for the connection. When all of the retransmitted frames within a sequence have been uploaded to legacy buffers, TCP Stack 215 posts HOT buffers prior to sending the ACK. Posting the HOT buffers allows Buffer Upload Unit 745 to resume processing incoming frames for the connection using HOT buffers without requesting user buffers.
In step 930, CMD Unit 710 receives a PRB command from the command ring via DMA Engine 310. The PRB command includes a DCT index corresponding to an entry for a connection, and a sync bit, among other fields. In step 932, CMD Unit 710 reads CBT 715 using the index. In step 934, CMD Unit 710 determines if the sync request flag read from the entry in CBT 715 is set, and if so, in step 936 CMD Unit 710 determines if the sync bit in the PRB command is set. If, in step 934, CMD Unit 710 determines the “sync request” flag read from the entry in CBT 715 is not set, then CMD Unit 710 clears the entry's “sync request” flag in CBT 715 in step 938, and proceeds to step 940. When the “sync request” flag is cleared, the connection may be processed using HOT buffers. If, in step 936, CMD Unit 710 determines the sync bit in the PRB command is not set, the “sync request” flag is not cleared and the connection continues to be processed using legacy processing.
Transmit Engine 320 includes subunits for offloading outbound frame processing from TCP Stack 215. For example, Transmit Engine 320 may be configured to perform TCP segmentation, compute TCP and IPv4 checksums, and edit outbound frames to piggyback ACKs and include the most recent state data for a delegated connection (read from DCT 350). Updates to DCT 350 made by Driver 255 or Receive Engine 360 may be included in transmissions, as described further herein.
Field 1015 is an IP header, Field 1020 is a TCP header, and Field 1025 is segmented data. As persons skilled in the art will recognize, the format shown in
In step 1103, DMA Engine 310 reads the transmit buffer and outputs the transmit descriptor and transmit buffer to Transmit Engine 320. In step 1109, Transmit Engine 320 computes an IP checksum based on IP header data extracted from the prototype header. In step 1111, Transmit Engine 320 determines a portion of the data for transmission included in the transmit buffer based on the maximum segment size (set by the destination during connection setup) after segmentation. In step 1113, Transmit Engine 320 constructs a segment for transmission, as described further herein with regard to
In step 1131, Transmit Engine 320 computes a TCP checksum based on TCP header data extracted from the prototype header, connection state data read from DCT 350, and the portion of data for transmission in the current frame. The calculated checksum is stored in the frame's TCP header. In step 1133, Transmit Engine 320 updates a transmit SN stored in DCT 350 for the delegated connection by increasing the transmit SN by the difference between the size (in bytes) of the data included in the frame and the header sizes. In step 1135, Transmit Engine 320 outputs a constructed frame, including a computed TCP checksum, to Transmit Interface 330. Transmit Interface 330 outputs the constructed frame.
In step 1115, Transmit Engine 320 uses the DCT index received in step 1101 with the transmission request to determine if the transmission request corresponds to a delegated connection, and, if it does not, proceeds to step 1131 of
In step 1121, Transmit Engine 320 examines the control bits specifying processing options and determines if TCP Stack 215 requests Transmit Engine 320 to save the SN of the first byte of the frame in CDT 720. The saved SN is used in step 907 of
In step 1125, Transmit Engine 320 determines an ACK number for the constructed frame. When the ACK number received from TCP Stack 215 is later in the data stream than the DCT SN stored for the connection, Transmit Engine 320 sets the DCT SN to the ACK number received from TCP Stack 215. Transmit Engine 320 also sets the last ACK number stored for the connection in CDT 720 to the larger of the DCT SN or the ACK number received from TCP Stack 215.
In step 1127, Transmit Engine 320 determines if the TCP timestamp option is enabled by examining the connection state data stored for the delegated connection in CDT 720. When the TCP timestamp option is not enabled, Transmit Engine proceeds to step 1131 of
In step 1149, Receive Engine 360 computes an ACK difference that is the difference between the SN and the last ACK number (read from DCT 350). In step 1151 Receive Engine 360 determines if the ACK difference is greater than a limit, the limit programmed by TCP Stack 215 to trigger an ACK to a received frame. If the ACK difference is greater than the limit, Receive Engine 360 proceeds to step 1157. Otherwise, in step 1153, Receive Engine 360 determines if the DCT SN is greater than a threshold, the threshold being an incremental sequence number or a specific sequence number. If the DCT SN is greater than the threshold, Receive Engine 360 proceeds to step 1157. Otherwise, in step 1155, Receive Engine 360 determines if the previously described transmit ACK timer has expired, and, if not, the transmit ACK timer and the unACKnowledged count is updated. If, in step 1155, Receive Engine 360 determines the transmit ACK timer has expired, then in step 1157 Receive Engine 360 updates connection state data stored in DCT 350 for the delegated connection, e.g., clearing the unACKnowledged count, updating the last ACKnowledged number, updating the incremental sequence number, and the like. Receive Engine 360 also resets the transmit ACK timer. In step 1159, Receive Engine 360 signals Transmit Engine 320 to include an ACK in a frame for transmission, i.e., by piggyback an ACK.
HOT Unit 350 offloads TCP processing for received valid TCP frames for delegated connections while permitting flexibility for Driver 255 or TCP Stack 215 to determine thresholds for interrupts based on received ACKs and timers. The thresholds may be used to reduce interrupts, freeing CPU 110 to process other applications. Furthermore, HOT Unit 350 generates ACKs for transmission and edits outbound frames to piggyback ACKs, to compute TCP and IPv4 checksums, and to perform TCP segmentation. Timely generation and transmission of ACKs to a sender may keep the receive window open, improving bandwidth utilization and reducing unnecessary retransmissions during unidirectional and bidirectional communication. Finally, payload data uploads to user buffers in Application Memory Space 227 reduces the need to copy data from Driver Memory Space 235 to Application Memory Space 227. When user buffers are not available for a delegated connection and Receive FIFO 730 is full, legacy buffers may be used to upload received frames rather than not accepting incoming data. HOT Unit 250 does not rely on large amounts of dedicated memory or a dedicated processor while providing offloading for some TCP processing from CPU 110. Hot Unit 250 also offloads some TCP processing from a host processor and handles excess connections while accepting incoming data.
The invention has been described above with reference to specific embodiments. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the invention as set forth in the appended claims. The foregoing description and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense. The listing of steps in method claims do not imply performing the steps in any particular order, unless explicitly stated in the claim. Within the claims, element lettering (e.g., “a)”, “b)”, “i)”, “ii)”, etc.) does not indicate any specific order for carrying out steps or other operations; the lettering is included to simplify referring to those elements.
This application claims priority from commonly owned co-pending provisional U.S. Patent Application No. 60/476,570 entitled “HARDWARE-OPTIMIZED TCP/IP (HOT) PROCESSING,” filed Jun. 5, 2003, having common inventors and assignee as this application, which is incorporated by reference as though fully set forth herein.
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