# Patent

## Title
Methods for the transmission of accelerator commands and corresponding command structure to remote hardware accelerator engines over an interconnect link

## Abstract

An apparatus and method of submitting hardware accelerator engine commands over an interconnect link such as a PCI Express (PCIe) link. In one embodiment, the mechanism is implemented inside a PCIe Host Bridge which is integrated into a host IC or chipset. The mechanism provides an interface compatible with other integrated accelerators thereby eliminating the overhead of maintaining different programming models for local and remote accelerators. Co-processor requests issued by threads requesting a service (client threads) targeting a remote accelerator are queued and sent to a PCIe adapter and remote accelerator engine over a PCIe link. The remote accelerator engine performs the requested processing task, delivers results back to host memory and the PCIe Host Bridge performs a co-processor request completion sequence (status update, write to flag, interrupt) included in the co-processor command.

## Background
FIELD OF THE INVENTION
The present invention relates to the field of data communications, and more particularly relates to an apparatus and method of submitting hardware accelerator engine commands over an interconnect link such as a Peripheral Component Interconnect (PCI) Express (PCIe) link.
SUMMARY OF THE INVENTION
There is thus provided in accordance with the invention, a method of submitting co-processor commands across an interconnect link, said method comprising generating a co-processor command structure in a region of main memory, issuing an accelerator command operative to transfer said co-processor command structure to an execution queue within a host bridge, retrieving source data associated with said accelerator command from memory, and transmitting said accelerator command, associated data and co-processor command structure to a remote hardware accelerator engine via said interconnect link.
There is also provided in accordance with the invention, a method of submitting co-processor commands across a PCIe link to a remote hardware accelerator engine, said method comprising generating co-processor commands at a PCIe host bridge for execution on a remote hardware accelerator engine coupled to a PCIe endpoint adaptor, and submitting said co-processor commands across a PCIe link to said PCIe endpoint adapter for execution on said remote hardware accelerator engine.
There is further provided in accordance with the invention, a method of submitting co-processor commands across an interconnect link to a remote hardware accelerator engine, said method comprising receiving an accelerator command over said interconnect link from a host bridge at an endpoint adapter and storing said accelerator command in an execution queue, executing said accelerator command read from said execution queue on said remote hardware accelerator engine, and sending processing results of said accelerator command execution back to said host bridge.
There is also provided in accordance with the invention, a method of submitting co-processor commands across a PCIe link to a remote hardware accelerator engine, said method comprising generating co-processor commands at a PCIe host bridge for execution on a remote hardware accelerator engine coupled to a PCIe endpoint adaptor, and submitting said co-processor commands across a PCIe link to said PCIe endpoint adapter for execution on said remote hardware accelerator engine, executing said co-processor commands on said remote hardware accelerator engine, and sending any processing execution results of said co-processor commands back to said PCIe host bridge.



BRIEF DESCRIPTION OF THE DRAWINGS
The invention is herein described, by way of example only, with reference to the accompanying drawings, wherein:
FIG. 1 is a block diagram illustrating an example PCIe attached accelerator emulation mechanism of the present invention;
FIG. 2 is a block diagram illustrating the example PCIe host bridge of FIG. 1 with PCIe port modifications in more detail in accordance with the accelerator emulation mechanism of the present invention;
FIG. 3 is a block diagram illustrating the example PCIe adapter port of FIG. 1 in more detail in accordance with the accelerator emulation mechanism of the present invention;
FIG. 4 is a flow diagram illustrating the host bridge side command submission method of the present invention;
FIG. 5 is a flow diagram illustrating the adapter port side command submission method of the present invention;
FIG. 6 is a diagram illustrating an example accelerator command structure; and
FIG. 7 is a diagram illustrating an example synchronization command.



DETAILED DESCRIPTION OF THE INVENTION
Processor offload is a commonly used model where various computational tasks may be offloaded from the CPU to a dedicated device optimized for specific tasks execution, typically some type of hardware accelerator. The accelerator core may be integrated together with the processor core on the same device or implemented as a standalone device attached via an interconnect technology such as a PCIe interface. In many applications today, remote PCIe-attached accelerators require a different programming model, due to the different nature of PCIe adapters.
Existing integration trends of multiple general processor cores with optimized task-oriented acceleration hardware allow for a significant increase in computational capacity for parallelized applications. Such architectures are often referred to as hybrid computing architectures. Typically, hardware based accelerator engines are tightly managed by software running on one of the generic processor cores and cannot be utilized without involvement of this management software. The architecture defines dedicated instructions, i.e. co-processor commands, that are used by software to communicate with the one or more hardware acceleration engines.
Many systems today are comprised of multiple devices where application software may run on one device but hardware acceleration engines intended to be used for offloading computations are located on a remote device. A typical system comprises a generic host device and a computation offload device, as described above, attached via an interconnection technology such as a PCIe connection. In such a system, software running on the host cannot access the remote acceleration engine directly and needs to communicate with the management software running on the remote device. Management software issues co-processor requests to the acceleration engine on behalf of the application software running on the host and reports results back to the host application upon completion of the accelerator task. This approach introduces a level of overhead when processing acceleration engine jobs initiated by external devices.
The accelerator emulation mechanism of the present invention is operative to represent a remote PCIe-attached accelerator as a locally integrated accelerator, while retaining a common programming model for both local and remote accelerators. The accelerator emulation mechanism allows software running on a general host processing device to engage remotely located acceleration engines directly without intervention of local management software by submitting accelerator co-processor commands across a communications interconnect such as a PCIe link.
In one embodiment, PCIe attached accelerators are part of the system structure and architecture. Alternatively, they can serve as a vehicle for prototyping new types of accelerators which can later be integrated into the general processor chip.
PCI Express was originally designed for desktops connecting a root complex (a host central processing unit (CPU) with memory) with downstream Input/Output (10) devices, but has since found applications in servers, storage devices, and other communications systems. The base PCIe switching structure of a single root complex has a tree topology, which addresses PCIe endpoints through a bus numbering scheme.
A block diagram illustrating an example PCIe attached accelerator emulation mechanism of the present invention is shown in FIG. 1. The system, generally referenced 10, comprises a host integrated circuit (IC) 12 in communication with a PCIe adapter 32 via a PCIe link 30. The PCIe adapter 32 includes a PCIe endpoint 34 and a remote accelerator engine 36. The host IC 12 comprises a plurality of general purpose CPU cores 14, memory and associated interface 16, one or more local accelerator cores 26 having a command queue 28, a PCIe host bridge 20 incorporating a command queue 22 and PCIe root port 24. The CPU cores, memory, local accelerator cores and PCIe host bridge communicate over coherent interconnect 18.
In one embodiment, the accelerator emulation mechanism is implemented inside a PCIe Host Bridge 20 which is integrated into the host IC or chipset. The accelerator emulation mechanism provides an interface compatible with other integrated accelerators thereby eliminating the overhead of maintaining different programming models for local and remote accelerators.
In an example embodiment, the accelerator emulation mechanism implements dedicated hardware (or software or a combination of hardware and software) that implements the following tasks. Co-processor requests issued by threads requesting a service (client threads) targeting a remote accelerator are queued. The PCIe Host Bridge provides command flow similar to conventional hardware accelerators. Co-processor commands are sent across the PCIe link 30 to the remote device (i.e. PCIe adapter endpoint) using PCIe posted write transactions. The remote accelerator engine pulls the required data from host memory, performs the requested processing task and delivers results back to host memory. The remote accelerator engine notifies the PCIe Host Bridge upon task completion. The PCIe Host Bridge performs a co-processor request completion sequence (status update, write to flag, interrupt). In one embodiment, the mechanism utilizes co-processor requests defined by the Power Architecture for interfacing hardware accelerator engines.
A block diagram illustrating the example PCIe host bridge of FIG. 1 with PCIe port modifications in more detail in accordance with the accelerator emulation mechanism of the present invention is shown in FIG. 2. The PCIe host bridge 40 comprises bus 51, host mapped memory input/output (MMIO) queues 48, Co-Processor Request Block (CRB) queues 50, data engine (direct memory access (DMA)) and acceleration control logic 52, DMA queues 54, interrupts 56, I/O memory mapping unit (IOMMU) 58 (hardware located in the host used to translate addresses of DMA transactions issued by the adapter), interrupt processing 60 and error handling and virtualization 62. The host bridge communicates with one or more general purpose CPU cores 42, memory 44 and one or more local accelerator engines 64 over coherent interconnect 46.
In operation, co-processor commands generated by the CPU cores are sent across the TX PCIe link 68 to the PCIe adapter and remote accelerator engine. Results of the execution of the co-processor commands are returned to the PCIe host bridge via RX PCIe link 70.
A block diagram illustrating the example PCIe adapter port of FIG. 1 in more detail in accordance with the accelerator emulation mechanism of the present invention is shown in FIG. 3. The PCIe adapter, generally referenced 80, comprises PCIe endpoint 86 and remote accelerator engine 96 in communication via coherent interconnect bus 94. The PCIe endpoint comprises DMA engine 88, Co-Processor Request Block (CRB) control register 90 and co-processor command buffer 92. Note that in one example embodiment, the CRB comprises a 64B data structure that contains commands for a co-processor (or accelerator). The remote accelerator engine 96 comprises one or more co-processors (hardware accelerators). In the example embodiment shown, the remote accelerator engine 96 comprises XML accelerator 98, regular expression accelerator 100, compression/decompression accelerator 102, general processor core 104 and local memory 106 all coupled to the coherent interconnect bus 94.
In operation, co-processor commands from the PCIe host bridge are received via MMIO writes from the host via TX PCIe link 84. Co-processor command completion results are sent back to the host bridge via RX PCIe link 82.
In one embodiment, the accelerator emulation mechanism comprises dedicated hardware implemented in the PCIe endpoint port logic that imitates management software behavior when issuing co-processor commands towards different remote acceleration engines. This hardware is assigned with software thread identifications, such as unique process ID (PID) and Logical Partition ID (LPID) numbers, that are used when issuing co-processor commands on its behalf. A combination of LPID/PID numbers identifies a software thread running in the system.
PCIe endpoint port logic comprises one or more local command buffers 92 (e.g., 64 bytes each) accessible by the host via the PCIe link interface 84. Host software running on the PCIe host bridge delivers the content of a co-processor command to the local buffer located in the PCIe adapter port and then triggers command execution by setting a control bit in a PCIe-mapped control register 90. The PCIe adapter port hardware generates co-processor commands based on local buffer content and locally assigned thread attributes and submits this command to local processor bus interconnect 94 for execution by the remote accelerator engine, as if this command was created by a software thread running on one of general processor cores of the host IC device.
In one embodiment, a co-processor command completion method of memory writes mapped back to PCIe upstream interface is used to signal command completion to the host IC. Additionally, the PCIe host bridge may use co-processor commands for engaging the PCIe adapter's DMA engine 88 for source and results data transfer between host and adapter local memory.
A flow diagram illustrating the host bridge side command submission method of the present invention is shown in FIG. 4. This host based method normally executes on the host IC side. Software on the host IC allocates memory for command structures, source data, destination data, status data, etc. in main memory (step 110). Local software on the host IC notifies the PCIe host bridge (via interrupt, predefined share memory buffer or other mechanism) that it is ready to accept acceleration commands (step 112). Software on the host IC prepares the command structure for a co-processor command in the pre-allocated region of the main memory (step 114). Software running on the PCIe host bridge delivers source data to local memory (using direct PCIe memory writes or by engaging local DMA engine).
Software running on the PCIe host bridge writes the CRB structure into a memory-mapped mailbox buffer (using regular PCIe memory write PCI Express Transaction Layer Packet (TLPs) used to convey application data over a PCIe link) (step 116). When a command structure is ready, software issues an accelerator command that triggers transfer of CRB structure on the interconnect crossbar (step 118). The PCIe host bridge writes to memory-mapped control register to trigger command submission.
When command submission trigger received, PCIe port logic pulls the CRB structure from the command buffer and delivers it to the crossbar interconnect. PCIe port logic receives co-processor commands from the interconnect crossbar and queues it for execution (step 120). The PCIe port data engine fetches source data from memory and sends it to acceleration engine over the TX PCIe link to the target accelerator engine (step 122).
A flow diagram illustrating the adapter port side command submission method of the present invention is shown in FIG. 5. The PCIe adapter endpoint receives the co-processor command over the PCIe link. PCIe adapter endpoint port logic triggers acceleration logic processing via application specific mechanism (e.g., by writing to the control register) (step 130). The remote accelerator engine then queues the co-processor command for execution (step 134). Command delivery status in the PCIe adapter endpoint port is updated, allowing submission of new co-processor commands (step 136). The co-processor command is executed by the remote accelerator engine (step 138).
When the target accelerator engine completes command execution, the acceleration logic reports acceleration task completion to PCIe adapter port logic (step 140). PCIe adapter port logic then executes any completion directive included in the original co-processor command (step 142). This directive may specify sending an interrupt back to the PCIe host bridge over the PCIe link indicating command completion to host IC software or writing to a reserved location being monitored by host IC software (step 144). Software running on the PCIe host bridge retrieves processing results (e.g., using direct PCIe memory reads or by engaging local DMA engine) and may take further action based on the results.
A diagram illustrating an example accelerator command structure is shown in FIG. 6. The command structure, generally referenced 150, comprising 64 bytes, comprises an optional channel command word (CCW) field 152, marker trace tag 154, control flags 156, command header (CH) field 158, serial number (SN) field 160, status area address (session ID) field 162, source Data Descriptor Entry (DDE) 164, destination (target) DDE 166 and Co-processor Completion Block (CCB) 168. In one example embodiment, the source DDE comprises a 16B data structure identifying the data range in the memory (i.e. starting address and size). DDEs are included in a CRB to specify source and destination data ranges for co-processor commands. In one example embodiment, the CCB comprises a 16B data structure identifying the method of co-processor notification. The CCB is also included in a CRB to specify the method for notification of co-processor command execution completion.
In an example embodiment, the command structure 150 can be used as a data transfer command (DMA), Regular Expression Pattern Matching engine command, encryption/decryption engine command, compression/decompression engine command, etc.
The Session ID represents the commands stream identifier (acceleration engine supports several concurrent streams). The Source DDE represents the source data descriptor and specifies memory location and total size of source data. The target DDE represents the destination data descriptor, specifies memory location where results of accelerator engine processing should be stored. The CCB field represents a completion directive, and specifies notification method(s) of command completion (e.g., memory writes to predefined location, interrupt, etc.).
A diagram illustrating an example synchronization command is shown in FIG. 7. The example synchronization command, generally referenced 170, comprises an optional CCW field 172, marker trace tag 174, status area address (session ID) 176, a plurality of reserved fields 178 and CCB field 180.
In operation, the synchronization command when completed indicates that all previously issued commands have completed. It is sent from the PCIe adapter to the PCIe host bridge in the host IC.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
The corresponding structures, materials, acts, and equivalents of all means or step plus function elements in the claims below are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description of the present invention has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the invention in the form disclosed. As numerous modifications and changes will readily occur to those skilled in the art, it is intended that the invention not be limited to the limited number of embodiments described herein. Accordingly, it will be appreciated that all suitable variations, modifications and equivalents may be resorted to, falling within the spirit and scope of the present invention. The embodiments were chosen and described in order to best explain the principles of the invention and the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated.

## Claims

1. A method of submitting an accelerator command across an interconnect link, the method comprising:
generating an accelerator command structure in a region of main memory of a host device, wherein the accelerator command structure includes: a channel command word (CCW) field, a marker trace tag; one or more control flags, a command header (CH) field, a serial number (SN) field, a status area address field, a source data descriptor entry (DDE), a target DDE, and a co-processor completion block (CCB) field;
issuing the accelerator command, wherein the accelerator command triggers transfer of the accelerator command structure to an execution queue within a host bridge of the host device;
retrieving source data associated with the accelerator command from the region of main memory; and
transmitting the accelerator command, the associated source data and the accelerator command structure to a remote hardware accelerator engine via the interconnect link.

2. The method according to claim 1, wherein the interconnect link comprises a Peripheral Component Interconnect Express (PCIe) link.

3. The method according to claim 1, wherein generating the accelerator command structure comprises allocating memory for source data, destination data, and status data related to the accelerator command.

4. The method according to claim 1, wherein issuing the accelerator command comprises writing the accelerator command structure into a memory mapped mailbox buffer using Peripheral Component Interconnect Express (PCIe) posted memory write Translation Layer Packets (TLPs).

5. The method according to claim 1, wherein the accelerator command, the associated source data and the accelerator command structure are transmitted to the remote hardware accelerator engine in response to an accelerator command submission trigger.

6. The method according to claim 1, further comprising: receiving accelerator request task completion results from the remote hardware accelerator engine; and performing an accelerator request completion sequence in response to receiving the accelerator request task completion results from the remote hardware accelerator engine.

7. The method according to claim 1, further comprising controlling communications between the host bridge and the remote hardware accelerator engine.

8. The method according to claim 1, wherein the accelerator command structure comprises 64 bytes.

9. The method according to claim 1, wherein the accelerator command is selected from a group consisting of: a data transfer command, a regular expression pattern matching command, a synchronization command, a compression engine command, and a decompression engine command.

10. A method of submitting an accelerator command across a Peripheral Component Interconnect Express (PCIe) link to a remote hardware accelerator engine, the method comprising:
allocating a region of main memory of a host device for a 64-byte accelerator command structure;
generating the 64-byte accelerator command structure in the allocated region of the main memory;
issuing the accelerator command, wherein issuing the accelerator command triggers transfer of the 64-byte accelerator command structure to an execution queue within a PCIe host bridge of the host device; and
submitting the accelerator command and the 64-byte accelerator command structure across the PCIe link to a PCIe endpoint for execution of the accelerator command on the remote hardware accelerator engine, the remote hardware accelerator engine being operatively coupled to the PCIe endpoint.

11. A method, comprising:
receiving an accelerator command structure and an accelerator command over an interconnect link from a host bridge of a host device at an endpoint, wherein the accelerator command is triggered by one or more threads requesting a service to be performed on a remote hardware accelerator engine operatively coupled to the endpoint, wherein the accelerator command structure is configured to provide a common programming model for the remote hardware accelerator engine and the host device, and wherein the accelerator command structure comprises:
a channel command word (CCW) field;
a marker trace tag;
one or more control flags,
a command header (CH) field;
a serial number (SN) field;
a status area address field;
a source data descriptor entry (DDE);
a target DDE; and
a co-processor completion block (CCB) field,
wherein the source DDE and the CCB field each comprise a 16-byte data structure;

storing the accelerator command in an execution queue on the remote hardware accelerator engine;
executing the accelerator command from the execution queue; and
sending processing results of the accelerator command execution back to the host bridge,
wherein the remote hardware accelerator engine and one or more local hardware accelerator engines of the host device have a common programming model.

12. The method according to claim 11, wherein the interconnect link comprises a Peripheral Component Interconnect Express (PCIe) link, the host bridge comprises a PCIe host bridge, and the endpoint comprises a PCIe endpoint, wherein the PCIe endpoint comprises an accelerator command buffer having a 64-byte data structure.

13. The method according to claim 12, further comprising notifying the PCIe host bridge via the PCIe link upon execution completion of the accelerator command.

14. The method according to claim 13, further comprising updating accelerator command delivery status in the PCIe host bridge thereby allowing submission of new accelerator commands.

15. The method according to claim 11, wherein executing the accelerator command comprises retrieving data required to execute the accelerator command from a region of memory of the host device.

16. The method according to claim 11, wherein the accelerator command is selected from a group consisting of: a regular expression pattern matching command, a synchronization command, a compression engine command, and a decompression engine command.

17. A method of submitting an accelerator command across a Peripheral Component Interconnect Express (PCIe) link to a remote hardware accelerator engine, the method comprising:
receiving a request from a thread requesting a service to be performed by the remote hardware accelerator engine;
generating an accelerator command structure in a region of main memory of a host device, wherein the accelerator command structure comprises:
a channel command word (CCW) field;
a marker trace tag;
one or more control flags,
a command header (CH) field;
a serial number (SN) field;
a status area address field;
a source data descriptor entry (DDE);
a target DDE; and
a co-processor completion block (CCB) field;

issuing the accelerator command, wherein the accelerator command triggers transfer of the accelerator command structure to an execution queue within a PCIe host bridge of the host device;
retrieving source data associated with the accelerator command from the main memory of the host device;
submitting the accelerator command structure, the accelerator command, and the source data associated with the accelerator command across the PCIe link to a PCIe endpoint for execution of the accelerator command on the remote hardware accelerator engine, the remote hardware accelerator engine being operatively coupled to the PCIe endpoint; and
receiving, at the PCIe host bridge, any processing execution results generated from execution of the accelerator command on the remote hardware accelerator engine,
wherein the PCIe endpoint comprises hardware assigned with thread identifications that are used when generating the accelerator command, the thread identifications including a combination of a unique process identifier (PID) and a Logical Partition identifier (LPID), and
wherein the accelerator command structure comprises 64 bytes.

18. The method according to claim 17, wherein the remote hardware accelerator engine effectively appears as a locally integrated accelerator to central processing unit (CPU) core processors connected to the PCIe host bridge.

19. The method according to claim 17, wherein the method effectively enables software executing on the PCIe host bridge to interface with a remote hardware accelerator engine at a PCIe endpoint without requiring any direct intervention of local management software.

20. The method according to claim 17, further comprising performing an accelerator command completion sequence in response to execution completion of the accelerator command by the remote hardware accelerator engine.

21. The method according to claim 17, wherein the source DDE and the CCB field each comprise a 16-byte data structure.