From: "H.J. Lu" <hjl.tools@gmail.com>
To: Noah Goldstein <goldstein.w.n@gmail.com>
Cc: GNU C Library <libc-alpha@sourceware.org>
Subject: Re: [PATCH] x86: Set rep_movsb_threshold to 2112 on processors with FSRM
Date: Fri, 30 Apr 2021 16:50:56 -0700 [thread overview]
Message-ID: <CAMe9rOp3W50YZb3Vz_ujr8XEzmtH1mVL3W8_GPT5Gu4OjZ_0jg@mail.gmail.com> (raw)
In-Reply-To: <CAFUsyfJKMBsEcHE4_DkxmwokabAXSxY_q6=AFS3CgyoHjvGkvw@mail.gmail.com>
On Fri, Apr 30, 2021 at 3:59 PM Noah Goldstein <goldstein.w.n@gmail.com> wrote:
>
> On Fri, Apr 30, 2021 at 4:43 PM H.J. Lu via Libc-alpha
> <libc-alpha@sourceware.org> wrote:
> >
> > The glibc memcpy benchmark on Intel Core i7-1065G7 (Ice Lake) showed
> > that REP MOVSB became faster after 2112 bytes:
> >
> > Vector + REP MOVSB REP MOVSB
> > length=2112, align1=0, align2=0: 24.20 24.40
> > length=2112, align1=1, align2=0: 26.07 23.13
> > length=2112, align1=0, align2=1: 27.18 28.13
> > length=2112, align1=1, align2=1: 26.23 25.16
> > length=2176, align1=0, align2=0: 23.18 22.52
> > length=2176, align1=2, align2=0: 25.45 22.52
> > length=2176, align1=0, align2=2: 27.14 27.82
> > length=2176, align1=2, align2=2: 22.73 25.56
> > length=2240, align1=0, align2=0: 24.62 24.25
> > length=2240, align1=3, align2=0: 29.77 27.15
> > length=2240, align1=0, align2=3: 35.55 29.93
> > length=2240, align1=3, align2=3: 34.49 25.15
> > length=2304, align1=0, align2=0: 34.75 26.64
> > length=2304, align1=4, align2=0: 32.09 22.63
> > length=2304, align1=0, align2=4: 28.43 31.24
> >
>
> Do you know what is happening at:
> length=2304, align1=0, align2=4: 28.43 31.24
>
> Seems align2 > align1 gets worse for larger sizes as well.
>
> I.e from my Icelake (1 run):
> w/o
> Patch w/ Patch
> length=3648, align1=0, align2=25: 72.91 83.99
> length=3712, align1=0, align2=26: 72.52 84.92
> length=3776, align1=0, align2=27: 76.16 84.02
> length=3840, align1=0, align2=28: 75.44 90.13
> length=3904, align1=0, align2=29: 81.62 84.43
> length=3968, align1=0, align2=30: 76.82 93.39
> length=4032, align1=0, align2=31: 80.01 89.89
> length=4096, align1=0, align2=32: 72.89 97.50
On Intel Core i7-1165G7 (Tiger Lake), I got
Vector
REP MOVSB
length=2112, align1=0, align2=1: 45.21 43.69
length=2176, align1=0, align2=2: 45.20 45.82
length=2240, align1=0, align2=3: 53.46 51.41
length=2304, align1=0, align2=4: 47.65 48.28
length=2368, align1=0, align2=5: 50.10 48.27
length=2432, align1=0, align2=6: 50.10 50.70
length=2496, align1=0, align2=7: 52.54 50.71
length=2560, align1=0, align2=8: 52.83 53.15
length=2624, align1=0, align2=9: 64.98 53.15
length=2688, align1=0, align2=10: 54.98 55.59
length=2752, align1=0, align2=11: 57.43 55.59
length=2816, align1=0, align2=12: 57.87 58.03
length=2880, align1=0, align2=13: 61.97 58.03
length=2944, align1=0, align2=14: 71.97 60.79
length=3008, align1=0, align2=15: 65.02 60.47
length=3072, align1=0, align2=16: 65.39 63.23
length=3136, align1=0, align2=17: 72.54 62.92
length=3200, align1=0, align2=18: 69.91 65.39
length=3264, align1=0, align2=19: 73.38 65.39
length=3328, align1=0, align2=20: 73.50 67.81
length=3392, align1=0, align2=21: 76.81 67.81
length=3456, align1=0, align2=22: 76.88 70.79
length=3520, align1=0, align2=23: 80.30 71.07
length=3584, align1=0, align2=24: 80.25 72.69
length=3648, align1=0, align2=25: 84.58 73.01
length=3712, align1=0, align2=26: 85.02 75.13
length=3776, align1=0, align2=27: 87.51 75.14
length=3840, align1=0, align2=28: 87.20 77.67
length=3904, align1=0, align2=29: 89.82 77.99
length=3968, align1=0, align2=30: 102.59 80.45
length=4032, align1=0, align2=31: 92.38 80.60
length=4096, align1=0, align2=32: 85.69 84.69
REP MOVSB is a little bit faster.
> > Use REP MOVSB for data size > 2112 bytes in memcpy on processors with
> > fast short REP MOVSB (FSRM).
> >
> > * sysdeps/x86/dl-cacheinfo.h (dl_init_cacheinfo): Set
> > rep_movsb_threshold to 2112 on processors with fast short REP
> > MOVSB (FSRM).
> > ---
> > sysdeps/x86/dl-cacheinfo.h | 10 ++++++++--
> > 1 file changed, 8 insertions(+), 2 deletions(-)
> >
> > diff --git a/sysdeps/x86/dl-cacheinfo.h b/sysdeps/x86/dl-cacheinfo.h
> > index d9944250fc..3f04fb5019 100644
> > --- a/sysdeps/x86/dl-cacheinfo.h
> > +++ b/sysdeps/x86/dl-cacheinfo.h
> > @@ -871,7 +871,10 @@ dl_init_cacheinfo (struct cpu_features *cpu_features)
> > if (CPU_FEATURE_USABLE_P (cpu_features, AVX512F)
> > && !CPU_FEATURE_PREFERRED_P (cpu_features, Prefer_No_AVX512))
> > {
> > - rep_movsb_threshold = 2048 * (64 / 16);
> > + if (CPU_FEATURE_USABLE_P (cpu_features, FSRM))
> > + rep_movsb_threshold = 2112;
> > + else
> > + rep_movsb_threshold = 2048 * (64 / 16);
> > #if HAVE_TUNABLES
> > minimum_rep_movsb_threshold = 64 * 8;
> > #endif
> > @@ -879,7 +882,10 @@ 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);
> > + if (CPU_FEATURE_USABLE_P (cpu_features, FSRM))
> > + rep_movsb_threshold = 2112;
> > + else
> > + rep_movsb_threshold = 2048 * (32 / 16);
> > #if HAVE_TUNABLES
> > minimum_rep_movsb_threshold = 32 * 8;
> > #endif
> > --
> > 2.31.1
> >
--
H.J.
next prev parent reply other threads:[~2021-04-30 23:51 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-30 18:24 H.J. Lu
2021-04-30 22:59 ` Noah Goldstein
2021-04-30 23:50 ` H.J. Lu [this message]
2021-05-01 0:17 ` Noah Goldstein
2021-05-01 1:26 ` H.J. Lu
2021-05-01 14:08 ` [PATCH v2] " H.J. Lu
2021-05-01 18:45 ` Noah Goldstein
2022-04-27 23:56 ` Sunil Pandey
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