On Thu, Aug 06, 2020 at 05:35:00PM +0200, Ingo Molnar wrote:
- Dan Williams dan.j.williams@intel.com wrote:
On Thu, Aug 6, 2020 at 6:35 AM Ingo Molnar mingo@kernel.org wrote:
- kernel test robot rong.a.chen@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_mcsafe...
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.
It would be nice to double check this on the kernel-test-robot side as well, to make sure it's not a false positive.
Hi Ingo,
We recompiled the kernels with option "-falign-functions=32", and the regression still exists:
7476b91d4db369d8 a0ac629ebe7b3d248cb9380778 testcase/testparams/testbox ---------------- -------------------------- --------------------------- %stddev change %stddev \ | \ 22103 -43% 12551 fio-basic/2M-performance-2pmem-xfs-libaio-dax-50%-200s-read-200G-tb-ucode=0x5002f01/lkp-csl-2sp6 22103 -43% 12551 GEO-MEAN fio.read_iops
Best Regards, Rong Chen