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Re: [PATCH] x86_64: memset optimized with AVX512
- From: "H.J. Lu" <hjl dot tools at gmail dot com>
- To: Andrew Senkevich <andrew dot n dot senkevich at gmail dot com>
- Cc: libc-alpha <libc-alpha at sourceware dot org>
- Date: Fri, 11 Dec 2015 05:39:03 -0800
- Subject: Re: [PATCH] x86_64: memset optimized with AVX512
- Authentication-results: sourceware.org; auth=none
- References: <CAMXFM3v7K1bO8aUB=rVBzKqAZJuNrMBh5NuyszONtB-sZrXcgA at mail dot gmail dot com> <CAMe9rOrmhNzZTjX9XS2ONhTghCU-UXs3WmWzRWkXhWHCDZi8GQ at mail dot gmail dot com> <CAMXFM3uDEgQyfmJtVzp8QqYCEFJpYMTENhG3RMu26_R6eeAs3g at mail dot gmail dot com> <CAMe9rOrvjXqk6F-fWBy_f4R9Rw0+yzkeb5T63OXkAPiw7OXnGw at mail dot gmail dot com> <CAMXFM3vHyJXK=AWcgBSUWHE7HTHSvLER6DVx2joGdTBFEC528Q at mail dot gmail dot com>
On Fri, Dec 11, 2015 at 5:26 AM, Andrew Senkevich
<andrew.n.senkevich@gmail.com> wrote:
> 2015-12-10 22:34 GMT+03:00 H.J. Lu <hjl.tools@gmail.com>:
>> On Thu, Dec 10, 2015 at 10:28 AM, Andrew Senkevich
>> <andrew.n.senkevich@gmail.com> wrote:
>>>>> END (MEMSET)
>>>>> +libc_hidden_def (__memset_avx2)
>>>>
>>>> Why is this change needed? If it is needed, please submit
>>>> a separate patch.
>>>
>>> We can avoid this change if hide implementation, test and IFUNC branch
>>> under HAVE_AVX512_ASM_SUPPORT.
>>>
>>>> Should __memset_chk_avx512 also be provided?
>>>
>>> It will be the same as AVX2 version, is it really needed?
>>
>> __memset_chk_avx2 calls __memset_avx2. Don't you want
>> __memset_chk to call __memset_avx512, instead of __memset_avx2,
>> on KNL?
>
> Oh yes, surely we need it.
>
> Is patch below Ok for trunk?
>
> 2015-12-11 Andrew Senkevich <andrew.senkevich@intel.com>
>
> * sysdeps/x86_64/multiarch/Makefile (sysdep_routines): Added new file.
> * sysdeps/x86_64/multiarch/ifunc-impl-list.c: Added new tests.
> * sysdeps/x86_64/multiarch/memset-avx512.S: New file.
> * sysdeps/x86_64/multiarch/memset.S: Added new IFUNC branch.
> * sysdeps/x86_64/multiarch/memset_chk.S: Likewise.
>
> diff --git a/sysdeps/x86_64/multiarch/memset.S
> b/sysdeps/x86_64/multiarch/memset.S
> index dbc00d2..9f16b7e 100644
> --- a/sysdeps/x86_64/multiarch/memset.S
> +++ b/sysdeps/x86_64/multiarch/memset.S
> @@ -30,6 +30,13 @@ ENTRY(memset)
> HAS_ARCH_FEATURE (AVX2_Usable)
> jz 2f
> leaq __memset_avx2(%rip), %rax
> +#ifdef HAVE_AVX512_ASM_SUPPORT
> + HAS_ARCH_FEATURE (AVX512DQ_Usable)
> + jnz 2f
> + HAS_ARCH_FEATURE (AVX512F_Usable)
> + jz 2f
> + leaq __memset_avx512(%rip), %rax
> +#endif
> 2: ret
> END(memset)
> #endif
> diff --git a/sysdeps/x86_64/multiarch/memset_chk.S
> b/sysdeps/x86_64/multiarch/memset_chk.S
> index e2abb15..5115dfb 100644
> --- a/sysdeps/x86_64/multiarch/memset_chk.S
> +++ b/sysdeps/x86_64/multiarch/memset_chk.S
> @@ -30,6 +30,13 @@ ENTRY(__memset_chk)
> HAS_ARCH_FEATURE (AVX2_Usable)
> jz 2f
> leaq __memset_chk_avx2(%rip), %rax
> +#ifdef HAVE_AVX512_ASM_SUPPORT
> + HAS_ARCH_FEATURE (AVX512DQ_Usable)
> + jnz 2f
> + HAS_ARCH_FEATURE (AVX512F_Usable)
> + jz 2f
> + leaq __memset_chk_avx512(%rip), %rax
> +#endif
> 2: ret
> END(__memset_chk)
>
What is the purpose of checking AVX512DQ_Usable? To
avoid using it on SKX? Is __memset_avx512 slower than
__memset_avx2 on SKX?
--
H.J.