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An evaluation of using CCIX for cache-coherent host-FPGA interfacing

  • For a long time, most discrete accelerators have been attached to host systems using various generations of the PCI Express interface. However, with its lack of support for coherency between accelerator and host caches, fine-grained interactions require frequent cache-flushes, or even the use of inefficient uncached memory regions. The Cache Coherent Interconnect for Accelerators (CCIX) was the first multi-vendor standard for enabling cache-coherent host-accelerator attachments, and already is indicative of the capabilities of upcoming standards such as Compute Express Link (CXL). In our work, we compare and contrast the use of CCIX with PCIe when interfacing an ARM-based host with two generations of CCIX-enabled FPGAs. We provide both low-level throughput and latency measurements for accesses and address translation, as well as examine an application-level use-case of using CCIX for fine-grained synchronization in an FPGA-accelerated database system. We can show that especially smaller reads from the FPGA to the host can benefit from CCIX by having roughly 33% shorter latency than PCIe. Small writes to the host have a latency roughly 32% higher than PCIe, though, since they carry a higher coherency overhead. For the database use-case, the use of CCIX allowed to maintain a constant synchronization latency even with heavy host-FPGA parallelism.

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Author of HS ReutlingenBernhardt, Arthur; Petrov, Ilia
Erschienen in:2022 IEEE 30th International Symposium on Field-Programmable Custom Computing Machines : FFCM 2022, 15-18 May 2022, New York, proceedings
Place of publication:Piscataway, NJ
Document Type:Conference Proceeding
Year of Publication:2022
Tag:database systems; memory management; parallel processing; programming; synchronization; throughput
Page Number:9
DDC classes:004 Informatik
Open Access?:Nein
Licence (German):License Logo  Lizenzbedingungen IEEE