Re: [x86/copy_mc] a0ac629ebe: fio.read_iops -43.3% regression
On Thu, Aug 6, 2020 at 6:35 AM Ingo Molnar <mingo(a)kernel.org> wrote:
* kernel test robot <rong.a.chen(a)intel.com> wrote:
> Greeting,
>
> FYI, we noticed a -43.3% regression of fio.read_iops due to commit:
>
>
> commit: a0ac629ebe7b3d248cb93807782a00d9142fdb98 ("x86/copy_mc: Introduce
copy_mc_generic()")
> url:
https://github.com/0day-ci/linux/commits/Dan-Williams/Renovate-memcpy_mcs...
>
>
> in testcase: fio-basic
> on test machine: 96 threads Intel(R) Xeon(R) Gold 6252 CPU @ 2.10GHz with 256G
memory
> with following parameters:
So this performance regression, if it isn't a spurious result, looks
concerning. Is this expected?
This is not expected and I think delays these patches until I'm back
from leave in a few weeks. I know that we might lose some inlining
effect due to replacing native memcpy, but I did not expect it would
have an impact like this. In my testing I was seeing a performance
improvement from replacing the careful / open-coded copy with rep;
mov;, which increases the surprise of this result.