Re: [PATCH] crypto: x86/crc32c-intel - Don't match some Zhaoxin CPUs

[Tony W Wang-oc]

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-oc@xxxxxxxxxxx>
>>>
>>> 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.

Sincerely
Tony