From: Noah Goldstein <goldstein.w.n@gmail.com>
To: GNU C Library <libc-alpha@sourceware.org>
Subject: Re: [PATCH v3 5/6] x86: Remove memcmp-sse4.S
Date: Sat, 9 Apr 2022 19:48:53 -0500 [thread overview]
Message-ID: <CAFUsyfKsapjC7wR3prHVpDhAZsQb3SerzTTFBN_nEaLQv8dcRQ@mail.gmail.com> (raw)
In-Reply-To: <20220410004250.1448020-5-goldstein.w.n@gmail.com>
Disregard this patch. It's from the wrong patchset.
On Sat, Apr 9, 2022 at 7:46 PM Noah Goldstein <goldstein.w.n@gmail.com> wrote:
>
> Code didn't actually use any sse4 instructions. The new memcmp-sse2
> implementation is also faster.
>
> geometric_mean(N=20) of page cross cases SSE2 / SSE4: 0.905
>
> Note there are two regressions prefering SSE2 for Size = 1 and Size =
> 65.
>
> Size = 1:
> size, align0, align1, ret, New Time/Old Time
> 1, 1, 1, 0, 1.2
> 1, 1, 1, 1, 1.197
> 1, 1, 1, -1, 1.2
>
> This is intentional. Size == 1 is significantly less hot based on
> profiles of GCC11 and Python3 than sizes [4, 8] (which is made
> hotter).
>
> Python3 Size = 1 -> 13.64%
> Python3 Size = [4, 8] -> 60.92%
>
> GCC11 Size = 1 -> 1.29%
> GCC11 Size = [4, 8] -> 33.86%
>
> size, align0, align1, ret, New Time/Old Time
> 4, 4, 4, 0, 0.622
> 4, 4, 4, 1, 0.797
> 4, 4, 4, -1, 0.805
> 5, 5, 5, 0, 0.623
> 5, 5, 5, 1, 0.777
> 5, 5, 5, -1, 0.802
> 6, 6, 6, 0, 0.625
> 6, 6, 6, 1, 0.813
> 6, 6, 6, -1, 0.788
> 7, 7, 7, 0, 0.625
> 7, 7, 7, 1, 0.799
> 7, 7, 7, -1, 0.795
> 8, 8, 8, 0, 0.625
> 8, 8, 8, 1, 0.848
> 8, 8, 8, -1, 0.914
> 9, 9, 9, 0, 0.625
>
> Size = 65:
> size, align0, align1, ret, New Time/Old Time
> 65, 0, 0, 0, 1.103
> 65, 0, 0, 1, 1.216
> 65, 0, 0, -1, 1.227
> 65, 65, 0, 0, 1.091
> 65, 0, 65, 1, 1.19
> 65, 65, 65, -1, 1.215
>
> This is because A) the checks in range [65, 96] are now unrolled 2x
> and B) because smaller values <= 16 are now given a hotter path. By
> contrast the SSE4 version has a branch for Size = 80. The unrolled
> version has get better performance for returns which need both
> comparisons.
>
> size, align0, align1, ret, New Time/Old Time
> 128, 4, 8, 0, 0.858
> 128, 4, 8, 1, 0.879
> 128, 4, 8, -1, 0.888
>
> As well, out of microbenchmark environments that are not full
> predictable the branch will have a real-cost.
> ---
> sysdeps/x86_64/multiarch/Makefile | 2 --
> sysdeps/x86_64/multiarch/ifunc-impl-list.c | 4 ----
> sysdeps/x86_64/multiarch/ifunc-memcmp.h | 4 ----
> 3 files changed, 10 deletions(-)
>
> diff --git a/sysdeps/x86_64/multiarch/Makefile b/sysdeps/x86_64/multiarch/Makefile
> index b573966966..0400ea332b 100644
> --- a/sysdeps/x86_64/multiarch/Makefile
> +++ b/sysdeps/x86_64/multiarch/Makefile
> @@ -11,7 +11,6 @@ sysdep_routines += \
> memcmp-avx2-movbe-rtm \
> memcmp-evex-movbe \
> memcmp-sse2 \
> - memcmp-sse4 \
> memcmpeq-avx2 \
> memcmpeq-avx2-rtm \
> memcmpeq-evex \
> @@ -164,7 +163,6 @@ sysdep_routines += \
> wmemcmp-avx2-movbe-rtm \
> wmemcmp-evex-movbe \
> wmemcmp-sse2 \
> - wmemcmp-sse4 \
> # sysdep_routines
> endif
>
> diff --git a/sysdeps/x86_64/multiarch/ifunc-impl-list.c b/sysdeps/x86_64/multiarch/ifunc-impl-list.c
> index c6008a73ed..a8afcf81bb 100644
> --- a/sysdeps/x86_64/multiarch/ifunc-impl-list.c
> +++ b/sysdeps/x86_64/multiarch/ifunc-impl-list.c
> @@ -96,8 +96,6 @@ __libc_ifunc_impl_list (const char *name, struct libc_ifunc_impl *array,
> && CPU_FEATURE_USABLE (BMI2)
> && CPU_FEATURE_USABLE (MOVBE)),
> __memcmp_evex_movbe)
> - IFUNC_IMPL_ADD (array, i, memcmp, CPU_FEATURE_USABLE (SSE4_1),
> - __memcmp_sse4_1)
> IFUNC_IMPL_ADD (array, i, memcmp, 1, __memcmp_sse2))
>
> #ifdef SHARED
> @@ -809,8 +807,6 @@ __libc_ifunc_impl_list (const char *name, struct libc_ifunc_impl *array,
> && CPU_FEATURE_USABLE (BMI2)
> && CPU_FEATURE_USABLE (MOVBE)),
> __wmemcmp_evex_movbe)
> - IFUNC_IMPL_ADD (array, i, wmemcmp, CPU_FEATURE_USABLE (SSE4_1),
> - __wmemcmp_sse4_1)
> IFUNC_IMPL_ADD (array, i, wmemcmp, 1, __wmemcmp_sse2))
>
> /* Support sysdeps/x86_64/multiarch/wmemset.c. */
> diff --git a/sysdeps/x86_64/multiarch/ifunc-memcmp.h b/sysdeps/x86_64/multiarch/ifunc-memcmp.h
> index 44759a3ad5..c743970fe3 100644
> --- a/sysdeps/x86_64/multiarch/ifunc-memcmp.h
> +++ b/sysdeps/x86_64/multiarch/ifunc-memcmp.h
> @@ -20,7 +20,6 @@
> # include <init-arch.h>
>
> extern __typeof (REDIRECT_NAME) OPTIMIZE (sse2) attribute_hidden;
> -extern __typeof (REDIRECT_NAME) OPTIMIZE (sse4_1) attribute_hidden;
> extern __typeof (REDIRECT_NAME) OPTIMIZE (avx2_movbe) attribute_hidden;
> extern __typeof (REDIRECT_NAME) OPTIMIZE (avx2_movbe_rtm) attribute_hidden;
> extern __typeof (REDIRECT_NAME) OPTIMIZE (evex_movbe) attribute_hidden;
> @@ -46,8 +45,5 @@ IFUNC_SELECTOR (void)
> return OPTIMIZE (avx2_movbe);
> }
>
> - if (CPU_FEATURE_USABLE_P (cpu_features, SSE4_1))
> - return OPTIMIZE (sse4_1);
> -
> return OPTIMIZE (sse2);
> }
> --
> 2.25.1
>
next prev parent reply other threads:[~2022-04-10 0:49 UTC|newest]
Thread overview: 49+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-03-25 18:36 [PATCH v1 1/6] x86: Remove {w}memcmp-ssse3 Noah Goldstein
2022-03-25 18:36 ` [PATCH v1 2/6] x86: Remove str{n}{case}cmp-ssse3 Noah Goldstein
2022-03-25 19:55 ` H.J. Lu
2022-03-25 20:44 ` [PATCH v2 1/6] x86: Remove {w}memcmp-ssse3 Noah Goldstein
2022-03-25 20:44 ` [PATCH v2 2/6] x86: Remove str{n}{case}cmp-ssse3 Noah Goldstein
2022-03-25 20:44 ` [PATCH v2 3/6] x86: Remove mem{move|cpy}-ssse3 Noah Goldstein
2022-04-10 0:57 ` [PATCH v4 6/6] x86: Reduce code size of mem{move|pcpy|cpy}-ssse3 Noah Goldstein
2022-03-25 20:44 ` [PATCH v2 4/6] x86: Remove mem{move|cpy}-ssse3-back Noah Goldstein
2022-03-25 20:44 ` [PATCH v2 5/6] x86: Remove str{n}cat-ssse3 Noah Goldstein
2022-03-25 20:44 ` [PATCH v2 6/6] x86: Remove str{p}{n}cpy-ssse3 Noah Goldstein
2022-04-10 0:42 ` [PATCH v3 1/6] " Noah Goldstein
2022-04-10 0:48 ` Noah Goldstein
2022-04-10 0:42 ` [PATCH v3 2/6] x86: Remove mem{move|cpy}-ssse3-back Noah Goldstein
2022-04-10 0:48 ` Noah Goldstein
2022-04-10 0:42 ` [PATCH v3 3/6] x86: Reduce code size of Remove mem{move|pcpy|cpy}-ssse3 Noah Goldstein
2022-04-10 0:48 ` Noah Goldstein
2022-04-10 0:42 ` [PATCH v3 4/6] x86: Optimize memcmp SSE2 in memcmp.S Noah Goldstein
2022-04-10 0:48 ` Noah Goldstein
2022-04-10 0:42 ` [PATCH v3 5/6] x86: Remove memcmp-sse4.S Noah Goldstein
2022-04-10 0:48 ` Noah Goldstein [this message]
2022-04-10 0:42 ` [PATCH v3 6/6] x86: Cleanup page cross code in memcmp-avx2-movbe.S Noah Goldstein
2022-04-10 0:48 ` Noah Goldstein
2022-04-10 0:54 ` [PATCH v4 1/6] x86: Remove {w}memcmp-ssse3 Noah Goldstein
2022-04-10 0:54 ` [PATCH v4 2/6] x86: Remove str{n}{case}cmp-ssse3 Noah Goldstein
2022-04-10 0:54 ` [PATCH v4 3/6] x86: Remove str{n}cat-ssse3 Noah Goldstein
2022-04-10 0:54 ` [PATCH v4 4/6] x86: Remove str{p}{n}cpy-ssse3 Noah Goldstein
2022-04-10 0:54 ` [PATCH v4 5/6] x86: Remove mem{move|cpy}-ssse3-back Noah Goldstein
2022-04-14 16:47 ` [PATCH v5 1/6] x86: Remove {w}memcmp-ssse3 Noah Goldstein
2022-04-14 16:47 ` [PATCH v5 2/6] x86: Remove str{n}{case}cmp-ssse3 Noah Goldstein
2022-04-14 18:05 ` H.J. Lu
2022-04-14 16:47 ` [PATCH v5 3/6] x86: Remove str{n}cat-ssse3 Noah Goldstein
2022-04-14 18:06 ` H.J. Lu
2022-04-14 16:47 ` [PATCH v5 4/6] x86: Remove str{p}{n}cpy-ssse3 Noah Goldstein
2022-04-14 18:10 ` H.J. Lu
2022-04-14 16:47 ` [PATCH v5 5/6] x86: Remove mem{move|cpy}-ssse3-back Noah Goldstein
2022-04-14 18:13 ` H.J. Lu
2022-04-14 16:47 ` [PATCH v5 6/6] x86: Reduce code size of mem{move|pcpy|cpy}-ssse3 Noah Goldstein
2022-04-14 18:04 ` [PATCH v5 1/6] x86: Remove {w}memcmp-ssse3 H.J. Lu
2022-03-25 18:36 ` [PATCH v1 3/6] x86: Remove mem{move|cpy}-ssse3 Noah Goldstein
2022-03-25 19:56 ` H.J. Lu
2022-03-25 18:36 ` [PATCH v1 4/6] x86: Remove mem{move|cpy}-ssse3-back Noah Goldstein
2022-03-25 19:56 ` H.J. Lu
2022-03-25 18:36 ` [PATCH v1 5/6] x86: Remove str{n}cat-ssse3 Noah Goldstein
2022-03-25 19:57 ` H.J. Lu
2022-03-25 18:36 ` [PATCH v1 6/6] x86: Remove str{p}{n}cpy-ssse3 Noah Goldstein
2022-03-25 19:57 ` H.J. Lu
2022-03-25 19:54 ` [PATCH v1 1/6] x86: Remove {w}memcmp-ssse3 H.J. Lu
2022-03-25 20:34 ` Andreas Schwab
2022-03-25 20:40 ` Noah Goldstein
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