From: Noah Goldstein <goldstein.w.n@gmail.com>
To: "H.J. Lu" <hjl.tools@gmail.com>
Cc: GNU C Library <libc-alpha@sourceware.org>
Subject: Re: [PATCH v3 5/5] x86: Double size of ERMS rep_movsb_threshold in dl-cacheinfo.h
Date: Sat, 6 Nov 2021 13:34:00 -0500 [thread overview]
Message-ID: <CAFUsyfKxziLh8rUiy=49JPswix87J2djN=_sDWeqQDji2HRb-Q@mail.gmail.com> (raw)
In-Reply-To: <CAMe9rOpp67otgEaariXnLVmbak-TyHOVGs8Hg=k0B3Z5iVfFRg@mail.gmail.com>
On Sat, Nov 6, 2021 at 1:21 PM H.J. Lu <hjl.tools@gmail.com> wrote:
>
> On Sat, Nov 6, 2021 at 11:12 AM Noah Goldstein <goldstein.w.n@gmail.com> wrote:
> >
> > On Sat, Nov 6, 2021 at 12:57 PM H.J. Lu <hjl.tools@gmail.com> wrote:
> > >
> > > On Sat, Nov 6, 2021 at 10:39 AM Noah Goldstein via Libc-alpha
> > > <libc-alpha@sourceware.org> wrote:
> > > >
> > > > No bug.
> > > >
> > > > This patch doubles the rep_movsb_threshold when using ERMS. Based on
> > > > benchmarks the vector copy loop, especially now that it handles 4k
> > > > aliasing, is better for these medium ranged.
> > > >
> > > > On Skylake with ERMS:
> > > >
> > > > Size, Align1, Align2, dst>src,(rep movsb) / (vec copy)
> > > > 4096, 0, 0, 0, 0.975
> > > > 4096, 0, 0, 1, 0.953
> > > > 4096, 12, 0, 0, 0.969
> > > > 4096, 12, 0, 1, 0.872
> > > > 4096, 44, 0, 0, 0.979
> > > > 4096, 44, 0, 1, 0.83
> > > > 4096, 0, 12, 0, 1.006
> > > > 4096, 0, 12, 1, 0.989
> > > > 4096, 0, 44, 0, 0.739
> > > > 4096, 0, 44, 1, 0.942
> > > > 4096, 12, 12, 0, 1.009
> > > > 4096, 12, 12, 1, 0.973
> > > > 4096, 44, 44, 0, 0.791
> > > > 4096, 44, 44, 1, 0.961
> > > > 4096, 2048, 0, 0, 0.978
> > > > 4096, 2048, 0, 1, 0.951
> > > > 4096, 2060, 0, 0, 0.986
> > > > 4096, 2060, 0, 1, 0.963
> > > > 4096, 2048, 12, 0, 0.971
> > > > 4096, 2048, 12, 1, 0.941
> > > > 4096, 2060, 12, 0, 0.977
> > > > 4096, 2060, 12, 1, 0.949
> > > > 8192, 0, 0, 0, 0.85
> > > > 8192, 0, 0, 1, 0.845
> > > > 8192, 13, 0, 0, 0.937
> > > > 8192, 13, 0, 1, 0.939
> > > > 8192, 45, 0, 0, 0.932
> > > > 8192, 45, 0, 1, 0.927
> > > > 8192, 0, 13, 0, 0.621
> > > > 8192, 0, 13, 1, 0.62
> > > > 8192, 0, 45, 0, 0.53
> > > > 8192, 0, 45, 1, 0.516
> > > > 8192, 13, 13, 0, 0.664
> > > > 8192, 13, 13, 1, 0.659
> > > > 8192, 45, 45, 0, 0.593
> > > > 8192, 45, 45, 1, 0.575
> > > > 8192, 2048, 0, 0, 0.854
> > > > 8192, 2048, 0, 1, 0.834
> > > > 8192, 2061, 0, 0, 0.863
> > > > 8192, 2061, 0, 1, 0.857
> > > > 8192, 2048, 13, 0, 0.63
> > > > 8192, 2048, 13, 1, 0.629
> > > > 8192, 2061, 13, 0, 0.627
> > > > 8192, 2061, 13, 1, 0.62
> > > > ---
> > > > sysdeps/x86/dl-cacheinfo.h | 8 ++++----
> > > > 1 file changed, 4 insertions(+), 4 deletions(-)
> > > >
> > > > diff --git a/sysdeps/x86/dl-cacheinfo.h b/sysdeps/x86/dl-cacheinfo.h
> > > > index e6c94dfd02..ceb3b53828 100644
> > > > --- a/sysdeps/x86/dl-cacheinfo.h
> > > > +++ b/sysdeps/x86/dl-cacheinfo.h
> > > > @@ -866,12 +866,12 @@ dl_init_cacheinfo (struct cpu_features *cpu_features)
> > > > /* NB: The REP MOVSB threshold must be greater than VEC_SIZE * 8. */
> > > > unsigned int minimum_rep_movsb_threshold;
> > > > #endif
> > > > - /* NB: The default REP MOVSB threshold is 2048 * (VEC_SIZE / 16). */
> > > > + /* NB: The default REP MOVSB threshold is 4096 * (VEC_SIZE / 16). */
> > > > unsigned int rep_movsb_threshold;
> > > > if (CPU_FEATURE_USABLE_P (cpu_features, AVX512F)
> > > > && !CPU_FEATURE_PREFERRED_P (cpu_features, Prefer_No_AVX512))
> > > > {
> > > > - rep_movsb_threshold = 2048 * (64 / 16);
> > > > + rep_movsb_threshold = 4096 * (64 / 16);
> > > > #if HAVE_TUNABLES
> > > > minimum_rep_movsb_threshold = 64 * 8;
> > > > #endif
> > > > @@ -879,14 +879,14 @@ dl_init_cacheinfo (struct cpu_features *cpu_features)
> > > > else if (CPU_FEATURE_PREFERRED_P (cpu_features,
> > > > AVX_Fast_Unaligned_Load))
> > > > {
> > > > - rep_movsb_threshold = 2048 * (32 / 16);
> > > > + rep_movsb_threshold = 4096 * (32 / 16);
> > > > #if HAVE_TUNABLES
> > > > minimum_rep_movsb_threshold = 32 * 8;
> > > > #endif
> > > > }
> > > > else
> > > > {
> > > > - rep_movsb_threshold = 2048 * (16 / 16);
> > > > + rep_movsb_threshold = 4096 * (16 / 16);
> > > > #if HAVE_TUNABLES
> > > > minimum_rep_movsb_threshold = 16 * 8;
> > > > #endif
> > > > --
> > > > 2.25.1
> > > >
> > >
> > > You need to update comments for x86_rep_movsb_threshold
> > > in sysdeps/x86/dl-tunables.list
> >
> > Can do.
> >
> > Noticing that the original values were based on comparisons with SSE2 likely on
> > SnB or IVB. I don't have any indication that the 2048 value is not
> > optimal for those
> > processors. Should we keep 2048 / (VEC_SIZE / 16) for SSE2?
>
> Good idea. So change the threshold to 2048 * (VEC_SIZE / 16) *
> (VEC_SIZE / 16)?
Done and updated the comments explaining the thresholds.
>
> --
> H.J.
next prev parent reply other threads:[~2021-11-06 18:34 UTC|newest]
Thread overview: 46+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-11-01 5:49 [PATCH v1 1/5] string: Make tests birdirectional test-memcpy.c Noah Goldstein
2021-11-01 5:49 ` [PATCH v1 2/5] benchtests: Add additional cases to bench-memcpy.c and bench-memmove.c Noah Goldstein
2021-11-06 2:27 ` H.J. Lu
2021-11-01 5:49 ` [PATCH v1 3/5] benchtests: Add partial overlap case in bench-memmove-walk.c Noah Goldstein
2021-11-06 2:28 ` H.J. Lu
2021-11-01 5:49 ` [PATCH v1 4/5] x86: Optimize memmove-vec-unaligned-erms.S Noah Goldstein
2021-11-01 5:52 ` Noah Goldstein
2021-11-06 2:29 ` H.J. Lu
2021-11-01 5:49 ` [PATCH v1 5/5] x86: Double size of ERMS rep_movsb_threshold in dl-cacheinfo.h Noah Goldstein
2021-11-06 2:31 ` H.J. Lu
2021-11-06 4:39 ` Noah Goldstein
2021-11-06 12:04 ` H.J. Lu
2021-11-06 17:38 ` Noah Goldstein
2021-11-06 2:27 ` [PATCH v1 1/5] string: Make tests birdirectional test-memcpy.c H.J. Lu
2021-11-06 4:39 ` [PATCH v2 " Noah Goldstein
2021-11-06 4:39 ` [PATCH v2 2/5] benchtests: Add additional cases to bench-memcpy.c and bench-memmove.c Noah Goldstein
2021-11-06 4:39 ` [PATCH v2 3/5] benchtests: Add partial overlap case in bench-memmove-walk.c Noah Goldstein
2021-11-06 4:39 ` [PATCH v2 4/5] x86: Optimize memmove-vec-unaligned-erms.S Noah Goldstein
2021-11-06 4:39 ` [PATCH v2 5/5] x86: Double size of ERMS rep_movsb_threshold in dl-cacheinfo.h Noah Goldstein
2021-11-06 17:37 ` [PATCH v3 1/5] string: Make tests birdirectional test-memcpy.c Noah Goldstein
2021-11-06 17:37 ` [PATCH v3 2/5] benchtests: Add additional cases to bench-memcpy.c and bench-memmove.c Noah Goldstein
2021-11-06 17:37 ` [PATCH v3 3/5] benchtests: Add partial overlap case in bench-memmove-walk.c Noah Goldstein
2021-11-06 17:37 ` [PATCH v3 4/5] x86: Optimize memmove-vec-unaligned-erms.S Noah Goldstein
2021-11-06 17:37 ` [PATCH v3 5/5] x86: Double size of ERMS rep_movsb_threshold in dl-cacheinfo.h Noah Goldstein
2021-11-06 17:56 ` H.J. Lu
2021-11-06 18:11 ` Noah Goldstein
2021-11-06 18:21 ` H.J. Lu
2021-11-06 18:34 ` Noah Goldstein [this message]
2021-11-06 18:33 ` [PATCH v4 1/5] string: Make tests birdirectional test-memcpy.c Noah Goldstein
2021-11-06 18:33 ` [PATCH v4 2/5] benchtests: Add additional cases to bench-memcpy.c and bench-memmove.c Noah Goldstein
2021-11-06 19:12 ` H.J. Lu
2021-11-06 18:33 ` [PATCH v4 3/5] benchtests: Add partial overlap case in bench-memmove-walk.c Noah Goldstein
2021-11-06 19:11 ` H.J. Lu
2021-11-06 18:33 ` [PATCH v4 4/5] x86: Optimize memmove-vec-unaligned-erms.S Noah Goldstein
2021-11-06 19:11 ` H.J. Lu
2022-04-23 1:41 ` Sunil Pandey
2021-11-06 18:33 ` [PATCH v4 5/5] x86: Double size of ERMS rep_movsb_threshold in dl-cacheinfo.h Noah Goldstein
2021-11-06 19:10 ` H.J. Lu
2022-04-23 1:42 ` Sunil Pandey
2021-11-06 19:12 ` [PATCH v4 1/5] string: Make tests birdirectional test-memcpy.c H.J. Lu
2021-11-06 21:20 ` Noah Goldstein
2021-11-07 13:53 ` H.J. Lu
2021-12-07 21:10 ` Stafford Horne
2021-12-07 21:36 ` Noah Goldstein
2021-12-07 22:07 ` Stafford Horne
2021-12-07 22:13 ` Noah Goldstein
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