Messages in this thread | | | From | Ard Biesheuvel <> | Date | Sat, 12 Dec 2020 10:36:28 +0100 | Subject | Re: [PATCH] crypto: x86/crc32c-intel - Don't match some Zhaoxin CPUs |
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On Fri, 11 Dec 2020 at 20:07, Eric Biggers <ebiggers@kernel.org> 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-oc@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. >
This driver does not use CRC instructions, but carryless multiplication and aggregation. So I suppose the pclmulqdq instruction triggers some pathological performance limitation here.
That means the crct10dif driver probably needs the same treatment.
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