[PATCH] x86: Use AVX2 memcpy/memset on Skylake server [BZ #21396]

[H.J. Lu]

On Tue, Apr 18, 2017 at 11:37 AM, H.J. Lu <hongjiu.lu@intel.com> wrote:
> On Skylake server, AVX512 load/store instructions in memcpy/memset may
> lead to lower CPU turbo frequency in certain situations.  Use of AVX2
> in memcpy/memset has been observed to have improved overall performance
> in many workloads due to the higher frequency.
>
> Since AVX512ER is unique to Xeon Phi, this patch sets Prefer_No_AVX512
> if AVX512ER isn't available so that AVX2 versions of memcpy/memset are
> used on Skylake server.
>
> Any comments?
>
>
> H.J.
> ---
>         [BZ #21396]
>         * sysdeps/x86/cpu-features.c (init_cpu_features): Set
>         Prefer_No_AVX512 if AVX512ER isn't available.
>         * sysdeps/x86/cpu-features.h (bit_arch_Prefer_No_AVX512): New.
>         (index_arch_Prefer_No_AVX512): Likewise.
>         * sysdeps/x86_64/multiarch/memcpy.S (__new_memcpy): Don't use
>         AVX512 version if Prefer_No_AVX512 is set.
>         * sysdeps/x86_64/multiarch/memcpy_chk.S (__memcpy_chk):
>         Likewise.
>         * sysdeps/x86_64/multiarch/memmove.S (__libc_memmove): Likewise.
>         * sysdeps/x86_64/multiarch/memmove_chk.S (__memmove_chk):
>         Likewise.
>         * sysdeps/x86_64/multiarch/mempcpy.S (__mempcpy): Likewise.
>         * sysdeps/x86_64/multiarch/mempcpy_chk.S (__mempcpy_chk):
>         Likewise.
>         * sysdeps/x86_64/multiarch/memset.S (memset): Likewise.
>         * sysdeps/x86_64/multiarch/memset_chk.S (__memset_chk):
>         Likewise.

Since this issue has significant impact on Skylake server, I'd like to
backport it to 2.24 and 2.25 branches together with the prerequisite
patch.   Any comments

Thanks.

H.J.
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