Re: [PATCH 0/4] RISC-V CRC optimizations

Alexandre Ghiti
2025-03-10T12:44:23Z

Hi Eric,

On 02/03/2025 23:04, Eric Biggers wrote:
> On Sun, Mar 02, 2025 at 07:56:46PM +0100, Björn Töpel wrote:
>> Eric!
>>
>> Eric Biggers <ebiggers@kernel.org> writes:
>>
>>> On Sun, Feb 16, 2025 at 02:55:26PM -0800, Eric Biggers wrote:
>>>> This patchset is a replacement for
>>>> "[PATCH v4] riscv: Optimize crct10dif with Zbc extension"
>>>> (https://lore.kernel.org/r/20250211071101.181652-1-zhihang.shao.iscas@gmail.com/).
>>>> It adopts the approach that I'm taking for x86 where code is shared
>>>> among CRC variants. It replaces the existing Zbc optimized CRC32
>>>> functions, then adds Zbc optimized CRC-T10DIF and CRC64 functions.
>>>>
>>>> This new code should be significantly faster than the current Zbc
>>>> optimized CRC32 code and the previously proposed CRC-T10DIF code. It
>>>> uses "folding" instead of just Barrett reduction, and it also implements
>>>> Barrett reduction more efficiently.
>>>>
>>>> This applies to crc-next at
>>>> https://git.kernel.org/pub/scm/linux/kernel/git/ebiggers/linux.git/log/?h=crc-next.
>>>> It depends on other patches that are queued there for 6.15, so I plan to
>>>> take it through there if there are no objections.
>>>>
>>>> Tested with crc_kunit in QEMU (set CONFIG_CRC_KUNIT_TEST=y and
>>>> CONFIG_CRC_BENCHMARK=y), both 32-bit and 64-bit. I don't have real Zbc
>>>> capable hardware to benchmark this on, but the new code should work very
>>>> well; similar optimizations work very well on other architectures.
>>> Any feedback on this series from the RISC-V side?
>> I have not reviewed your series, but I did a testrun the Milk-V Jupiter
>> which sports a Spacemit K1 that has Zbc.
>>
>> I based the run on commit 1973160c90d7 ("Merge tag
>> 'gpio-fixes-for-v6.14-rc5' of
>> git://git.kernel.org/pub/scm/linux/kernel/git/brgl/linux"), plus your
>> crc-next branch (commit a0bd462f3a13 ("x86/crc: add ANNOTATE_NOENDBR to
>> suppress objtool warnings")) merged:
>>
>> | --- base1.txt 2025-03-02 18:31:16.169438876 +0000
>> | +++ eric.txt 2025-03-02 18:35:58.683017223 +0000
>> | @@ -11,7 +11,7 @@
>> | # crc16_benchmark: len=127: 153 MB/s
>> | # crc16_benchmark: len=128: 153 MB/s
>> | # crc16_benchmark: len=200: 153 MB/s
>> | - # crc16_benchmark: len=256: 153 MB/s
>> | + # crc16_benchmark: len=256: 154 MB/s
>> | # crc16_benchmark: len=511: 154 MB/s
>> | # crc16_benchmark: len=512: 154 MB/s
>> | # crc16_benchmark: len=1024: 155 MB/s
>> | @@ -20,94 +20,94 @@
>> | # crc16_benchmark: len=16384: 155 MB/s
>> | ok 2 crc16_benchmark
>> | ok 3 crc_t10dif_test
>> | - # crc_t10dif_benchmark: len=1: 48 MB/s
>> | - # crc_t10dif_benchmark: len=16: 125 MB/s
>> | - # crc_t10dif_benchmark: len=64: 136 MB/s
>> | - # crc_t10dif_benchmark: len=127: 138 MB/s
>> | - # crc_t10dif_benchmark: len=128: 138 MB/s
>> | - # crc_t10dif_benchmark: len=200: 138 MB/s
>> | - # crc_t10dif_benchmark: len=256: 138 MB/s
>> | - # crc_t10dif_benchmark: len=511: 139 MB/s
>> | - # crc_t10dif_benchmark: len=512: 139 MB/s
>> | - # crc_t10dif_benchmark: len=1024: 139 MB/s
>> | - # crc_t10dif_benchmark: len=3173: 140 MB/s
>> | - # crc_t10dif_benchmark: len=4096: 140 MB/s
>> | - # crc_t10dif_benchmark: len=16384: 140 MB/s
>> | + # crc_t10dif_benchmark: len=1: 28 MB/s
>> | + # crc_t10dif_benchmark: len=16: 236 MB/s
>> | + # crc_t10dif_benchmark: len=64: 450 MB/s
>> | + # crc_t10dif_benchmark: len=127: 480 MB/s
>> | + # crc_t10dif_benchmark: len=128: 540 MB/s
>> | + # crc_t10dif_benchmark: len=200: 559 MB/s
>> | + # crc_t10dif_benchmark: len=256: 600 MB/s
>> | + # crc_t10dif_benchmark: len=511: 613 MB/s
>> | + # crc_t10dif_benchmark: len=512: 635 MB/s
>> | + # crc_t10dif_benchmark: len=1024: 654 MB/s
>> | + # crc_t10dif_benchmark: len=3173: 665 MB/s
>> | + # crc_t10dif_benchmark: len=4096: 669 MB/s
>> | + # crc_t10dif_benchmark: len=16384: 673 MB/s
>> | ok 4 crc_t10dif_benchmark
>> | ok 5 crc32_le_test
>> | # crc32_le_benchmark: len=1: 31 MB/s
>> | - # crc32_le_benchmark: len=16: 456 MB/s
>> | - # crc32_le_benchmark: len=64: 682 MB/s
>> | - # crc32_le_benchmark: len=127: 620 MB/s
>> | - # crc32_le_benchmark: len=128: 744 MB/s
>> | - # crc32_le_benchmark: len=200: 768 MB/s
>> | - # crc32_le_benchmark: len=256: 777 MB/s
>> | - # crc32_le_benchmark: len=511: 758 MB/s
>> | - # crc32_le_benchmark: len=512: 798 MB/s
>> | - # crc32_le_benchmark: len=1024: 807 MB/s
>> | - # crc32_le_benchmark: len=3173: 807 MB/s
>> | - # crc32_le_benchmark: len=4096: 814 MB/s
>> | - # crc32_le_benchmark: len=16384: 816 MB/s
>> | + # crc32_le_benchmark: len=16: 439 MB/s
>> | + # crc32_le_benchmark: len=64: 1209 MB/s
>> | + # crc32_le_benchmark: len=127: 1067 MB/s
>> | + # crc32_le_benchmark: len=128: 1616 MB/s
>> | + # crc32_le_benchmark: len=200: 1739 MB/s
>> | + # crc32_le_benchmark: len=256: 1951 MB/s
>> | + # crc32_le_benchmark: len=511: 1855 MB/s
>> | + # crc32_le_benchmark: len=512: 2174 MB/s
>> | + # crc32_le_benchmark: len=1024: 2301 MB/s
>> | + # crc32_le_benchmark: len=3173: 2347 MB/s
>> | + # crc32_le_benchmark: len=4096: 2407 MB/s
>> | + # crc32_le_benchmark: len=16384: 2440 MB/s
>> | ok 6 crc32_le_benchmark
>> | ok 7 crc32_be_test
>> | - # crc32_be_benchmark: len=1: 27 MB/s
>> | - # crc32_be_benchmark: len=16: 258 MB/s
>> | - # crc32_be_benchmark: len=64: 388 MB/s
>> | - # crc32_be_benchmark: len=127: 402 MB/s
>> | - # crc32_be_benchmark: len=128: 424 MB/s
>> | - # crc32_be_benchmark: len=200: 438 MB/s
>> | - # crc32_be_benchmark: len=256: 444 MB/s
>> | - # crc32_be_benchmark: len=511: 449 MB/s
>> | - # crc32_be_benchmark: len=512: 455 MB/s
>> | - # crc32_be_benchmark: len=1024: 461 MB/s
>> | - # crc32_be_benchmark: len=3173: 463 MB/s
>> | - # crc32_be_benchmark: len=4096: 465 MB/s
>> | - # crc32_be_benchmark: len=16384: 466 MB/s
>> | + # crc32_be_benchmark: len=1: 25 MB/s
>> | + # crc32_be_benchmark: len=16: 251 MB/s
>> | + # crc32_be_benchmark: len=64: 458 MB/s
>> | + # crc32_be_benchmark: len=127: 496 MB/s
>> | + # crc32_be_benchmark: len=128: 547 MB/s
>> | + # crc32_be_benchmark: len=200: 569 MB/s
>> | + # crc32_be_benchmark: len=256: 605 MB/s
>> | + # crc32_be_benchmark: len=511: 621 MB/s
>> | + # crc32_be_benchmark: len=512: 637 MB/s
>> | + # crc32_be_benchmark: len=1024: 657 MB/s
>> | + # crc32_be_benchmark: len=3173: 668 MB/s
>> | + # crc32_be_benchmark: len=4096: 671 MB/s
>> | + # crc32_be_benchmark: len=16384: 674 MB/s
>> | ok 8 crc32_be_benchmark
>> | ok 9 crc32c_test
>> | # crc32c_benchmark: len=1: 31 MB/s
>> | - # crc32c_benchmark: len=16: 457 MB/s
>> | - # crc32c_benchmark: len=64: 682 MB/s
>> | - # crc32c_benchmark: len=127: 620 MB/s
>> | - # crc32c_benchmark: len=128: 744 MB/s
>> | - # crc32c_benchmark: len=200: 769 MB/s
>> | - # crc32c_benchmark: len=256: 779 MB/s
>> | - # crc32c_benchmark: len=511: 758 MB/s
>> | - # crc32c_benchmark: len=512: 797 MB/s
>> | - # crc32c_benchmark: len=1024: 807 MB/s
>> | - # crc32c_benchmark: len=3173: 806 MB/s
>> | - # crc32c_benchmark: len=4096: 813 MB/s
>> | - # crc32c_benchmark: len=16384: 816 MB/s
>> | + # crc32c_benchmark: len=16: 446 MB/s
>> | + # crc32c_benchmark: len=64: 1188 MB/s
>> | + # crc32c_benchmark: len=127: 1066 MB/s
>> | + # crc32c_benchmark: len=128: 1600 MB/s
>> | + # crc32c_benchmark: len=200: 1727 MB/s
>> | + # crc32c_benchmark: len=256: 1941 MB/s
>> | + # crc32c_benchmark: len=511: 1854 MB/s
>> | + # crc32c_benchmark: len=512: 2164 MB/s
>> | + # crc32c_benchmark: len=1024: 2300 MB/s
>> | + # crc32c_benchmark: len=3173: 2345 MB/s
>> | + # crc32c_benchmark: len=4096: 2402 MB/s
>> | + # crc32c_benchmark: len=16384: 2437 MB/s
>> | ok 10 crc32c_benchmark
>> | ok 11 crc64_be_test
>> | - # crc64_be_benchmark: len=1: 64 MB/s
>> | - # crc64_be_benchmark: len=16: 144 MB/s
>> | - # crc64_be_benchmark: len=64: 154 MB/s
>> | - # crc64_be_benchmark: len=127: 156 MB/s
>> | - # crc64_be_benchmark: len=128: 156 MB/s
>> | - # crc64_be_benchmark: len=200: 156 MB/s
>> | - # crc64_be_benchmark: len=256: 156 MB/s
>> | - # crc64_be_benchmark: len=511: 157 MB/s
>> | - # crc64_be_benchmark: len=512: 157 MB/s
>> | - # crc64_be_benchmark: len=1024: 157 MB/s
>> | - # crc64_be_benchmark: len=3173: 158 MB/s
>> | - # crc64_be_benchmark: len=4096: 158 MB/s
>> | - # crc64_be_benchmark: len=16384: 158 MB/s
>> | + # crc64_be_benchmark: len=1: 29 MB/s
>> | + # crc64_be_benchmark: len=16: 264 MB/s
>> | + # crc64_be_benchmark: len=64: 476 MB/s
>> | + # crc64_be_benchmark: len=127: 499 MB/s
>> | + # crc64_be_benchmark: len=128: 558 MB/s
>> | + # crc64_be_benchmark: len=200: 576 MB/s
>> | + # crc64_be_benchmark: len=256: 611 MB/s
>> | + # crc64_be_benchmark: len=511: 621 MB/s
>> | + # crc64_be_benchmark: len=512: 638 MB/s
>> | + # crc64_be_benchmark: len=1024: 659 MB/s
>> | + # crc64_be_benchmark: len=3173: 667 MB/s
>> | + # crc64_be_benchmark: len=4096: 671 MB/s
>> | + # crc64_be_benchmark: len=16384: 674 MB/s
>> | ok 12 crc64_be_benchmark
>> | ok 13 crc64_nvme_test
>> | - # crc64_nvme_benchmark: len=1: 64 MB/s
>> | - # crc64_nvme_benchmark: len=16: 144 MB/s
>> | - # crc64_nvme_benchmark: len=64: 154 MB/s
>> | - # crc64_nvme_benchmark: len=127: 156 MB/s
>> | - # crc64_nvme_benchmark: len=128: 156 MB/s
>> | - # crc64_nvme_benchmark: len=200: 156 MB/s
>> | - # crc64_nvme_benchmark: len=256: 156 MB/s
>> | - # crc64_nvme_benchmark: len=511: 157 MB/s
>> | - # crc64_nvme_benchmark: len=512: 157 MB/s
>> | - # crc64_nvme_benchmark: len=1024: 157 MB/s
>> | - # crc64_nvme_benchmark: len=3173: 158 MB/s
>> | - # crc64_nvme_benchmark: len=4096: 158 MB/s
>> | - # crc64_nvme_benchmark: len=16384: 158 MB/s
>> | + # crc64_nvme_benchmark: len=1: 36 MB/s
>> | + # crc64_nvme_benchmark: len=16: 479 MB/s
>> | + # crc64_nvme_benchmark: len=64: 1340 MB/s
>> | + # crc64_nvme_benchmark: len=127: 1179 MB/s
>> | + # crc64_nvme_benchmark: len=128: 1766 MB/s
>> | + # crc64_nvme_benchmark: len=200: 1965 MB/s
>> | + # crc64_nvme_benchmark: len=256: 2201 MB/s
>> | + # crc64_nvme_benchmark: len=511: 2087 MB/s
>> | + # crc64_nvme_benchmark: len=512: 2464 MB/s
>> | + # crc64_nvme_benchmark: len=1024: 2331 MB/s
>> | + # crc64_nvme_benchmark: len=3173: 2673 MB/s
>> | + # crc64_nvme_benchmark: len=4096: 2745 MB/s
>> | + # crc64_nvme_benchmark: len=16384: 2782 MB/s
>> | ok 14 crc64_nvme_benchmark
>> | # crc: pass:14 fail:0 skip:0 total:14
>> | # Totals: pass:14 fail:0 skip:0 total:14
>>
>> That's a significant speed up for this popular SoC, and it would be
>> great to get this series in for the next merge window! Thank you!
>>
>> Tested-by: Björn Töpel <bjorn@rivosinc.com>
> Thanks for testing this patchset! So to summarize, on long messages the results
> were roughly:
>
> lsb-first CRCs (crc32_le, crc32c, crc64_nvme):
> Generic table-based code: 158 MB/s
> Old Zbc-optimized code (crc32* only): 816 MB/s
> New Zbc-optimized code: 2440 MB/s
>
> mst-first CRCs (crc_t10dif, crc32_be, crc64_be):
> Generic table-based code: 158 MB/s
> Old Zbc-optimized code (crc32* only): 466 MB/s
> New Zbc-optimized code: 674 MB/s
>
> So, quite positive results. Though, the fact the msb-first CRCs are (still) so
> much slower than lsb-first ones indicates that be64_to_cpu() is super slow on
> RISC-V. That seems to be caused by the rev8 instruction from Zbb not being
> used. I wonder if there are any plans to make the endianness swap macros use
> rev8, or if I'm going to have to roll my own endianness swap in the CRC code.
> (I assume it would be fine for the CRC code to depend on both Zbb and Zbc.)
>
> Anyway, I've applied this series to the crc tree
> (https://web.git.kernel.org/pub/scm/linux/kernel/git/ebiggers/linux.git/log/?h=crc-next).
>
> Palmer, I'd appreciate your ack though!

Very hard to review but given Bjorn's tests on a Zbc platform, you can add:

Acked-by: Alexandre Ghiti <alexghiti@rivosinc.com>

Thank you very much for working on this and unveiling the issue with the
beXX_to_cpu() macros!

Alex

>
> - Eric
>
> _______________________________________________
> linux-riscv mailing list
> linux-riscv@lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-riscv