On December 16, 2020 1:56:45 AM GMT+08:00, Eric Biggers <ebigg...@kernel.org> wrote: >On Tue, Dec 15, 2020 at 10:15:29AM +0800, Tony W Wang-oc wrote: >> >> On 15/12/2020 04:41, Eric Biggers wrote: >> > On Mon, Dec 14, 2020 at 10:28:19AM +0800, Tony W Wang-oc wrote: >> >> On 12/12/2020 01:43, Eric Biggers wrote: >> >>> On Fri, Dec 11, 2020 at 07:29:04PM +0800, Tony W Wang-oc wrote: >> >>>> The driver crc32c-intel match CPUs supporting >X86_FEATURE_XMM4_2. >> >>>> On platforms with Zhaoxin CPUs supporting this X86 feature, When >> >>>> crc32c-intel and crc32c-generic are both registered, system will >> >>>> use crc32c-intel because its .cra_priority is greater than >> >>>> crc32c-generic. This case expect to use crc32c-generic driver >for >> >>>> some Zhaoxin CPUs to get performance gain, So remove these >Zhaoxin >> >>>> CPUs support from crc32c-intel. >> >>>> >> >>>> Signed-off-by: Tony W Wang-oc <tonywwang...@zhaoxin.com> >> >>> >> >>> Does this mean that the performance of the crc32c instruction on >those CPUs is >> >>> actually slower than a regular C implementation? That's very >weird. >> >>> >> >> >> >> From the lmbench3 Create and Delete file test on those chips, I >think yes. >> >> >> > >> > Did you try measuring the performance of the hashing itself, and >not some >> > higher-level filesystem operations? >> > >> >> Yes. Was testing on these Zhaoxin CPUs, the result is that with the >same >> input value the generic C implementation takes fewer time than the >> crc32c instruction implementation. >> > >And that is really "working as intended"?
These CPU's crc32c instruction is not working as intended. Why do these CPUs even >declare that >they support the crc32c instruction, when it is so slow? > The presence of crc32c and some other instructions supports are enumerated by CPUID.01:ECX[SSE4.2] = 1, other instructions are ok except the crc32c instruction. >Are there any other instruction sets (AES-NI, PCLMUL, SSE, SSE2, AVX, >etc.) that >these CPUs similarly declare support for but they are uselessly slow? No. Sincerely Tonyw > >- Eric
