RE: [PATCH v3 2/5] benchtests: Add memset zero fill benchtest

["Lucas A. M. Magalhaes via Libc-alpha" <libc-alpha@sourceware.org>]

Quoting naohirot@fujitsu.com (2021-09-12 21:53:22)
> Hi Lucas,
> 
> > From: Lucas A. M. Magalhaes <lamm@linux.ibm.com>
> > Sent: Saturday, September 11, 2021 5:40 AM
> > 
> > Thanks for working on this. Please, correct me if I'm wrong but I guess you sent
> > an old version by mistake. This patch is lacking the bench-variant
> > implementations mentioned on the commit message.
> 
> Thank you for the comment!
> I double checked the source code and confirmed it is the one I intended.
> 4 patterns are combination of json attribute "char1" and "char2".
> "char1" and "char2" varies 0 and 1 respectively.
> 
> zero-over-zero: char1=0, char2=0
> zero-over-one: char1=0, char2=1
> one-over-zero: char1=1, char2=0
> one-over-one: char1=1, char2=1
> 
> I made a comment inline too.
> 

Thanks for clarifying, now I got it. Please can you add a comment on the
code explaining this patterns and the reason behind them?

With that said this patch LGTM.

> BTW, could you review the patch "benchtests: Remove redundant assert.h" [1]
> that is reflected your comment [2] to other bench tests if you had time?
> 
> [1] https://sourceware.org/pipermail/libc-alpha/2021-August/129840.html
> [2] https://sourceware.org/pipermail/libc-alpha/2021-July/128989.html
> 
> > 
> > Quoting Naohiro Tamura (2021-08-05 04:50:53)
> > > Memset takes 0 as the second parameter in most cases.
> > > However, we cannot measure the zero fill performance by
> > > bench-memset.c, bench-memset-large.c and bench-memset-walk.c
> > > precisely.
> > > X86_64 micro-architecture has some zero-over-zero optimization, and
> > > AArch64 micro-architecture also has some optimization for DC ZVA
> > > instruction.
> > > This patch provides bench-memset-zerofill.c which is suitable to
> > > analyze the zero fill performance by comparing among 4 patterns,
> > > zero-over-zero, zero-over-one, one-over-zero and one-over-one, from
> > > 256B to 64MB(RAM) through L1, L2 and L3 caches.
> > >
> > > The following commands are examples to analyze a JSON output,
> > > bench-memset-zerofill.out, by 'jq' and 'plot_strings.py'.
> > >
> > > 1) compare zero-over-zero performance
> > >
> > > $ cat bench-memset-zerofill.out | \
> > >   jq -r '
> > >     .functions.memset."bench-variant"="zerofill-0o0" |
> > >     del(.functions.memset.results[] | select(.char1 != 0 or .char2 != 0))
> > >   ' | \
> > >   plot_strings.py -l -p thru -v -
> > >
> > > 2) compare zero paformance
> > >
> > > $ cat bench-memset-zerofill.out | \
> > >   jq -r '
> > >     .functions.memset."bench-variant"="zerofill-zero" |
> > >     del(.functions.memset.results[] | select(.char2 != 0))
> > >   ' | \
> > >   plot_strings.py -l -p thru -v -
> > >
> > > 3) compare nonzero paformance
> > >
> > > $ cat bench-memset-zerofill.out | \
> > >   jq -r '
> > >     .functions.memset."bench-variant"="zerofill-nonzero" |
> > >     del(.functions.memset.results[] | select(.char2 == 0))
> > >   ' | \
> > >   plot_strings.py -l -p thru -v -
> > > ---
> > >  benchtests/Makefile                |   2 +-
> > >  benchtests/bench-memset-zerofill.c | 134 +++++++++++++++++++++++++++++
> > >  2 files changed, 135 insertions(+), 1 deletion(-)
> > >  create mode 100644 benchtests/bench-memset-zerofill.c
> > >
> > > diff --git a/benchtests/Makefile b/benchtests/Makefile
> > > index 1530939a8ce8..21b95c736190 100644
> > > --- a/benchtests/Makefile
> > > +++ b/benchtests/Makefile
> > > @@ -53,7 +53,7 @@ string-benchset := memccpy memchr memcmp memcpy memmem memmove \
> > >                    strncasecmp strncat strncmp strncpy strnlen strpbrk strrchr \
> > >                    strspn strstr strcpy_chk stpcpy_chk memrchr strsep strtok \
> > >                    strcoll memcpy-large memcpy-random memmove-large memset-large \
> > > -                  memcpy-walk memset-walk memmove-walk
> > > +                  memcpy-walk memset-walk memmove-walk memset-zerofill
> > >
> > >  # Build and run locale-dependent benchmarks only if we're building natively.
> > >  ifeq (no,$(cross-compiling))
> > > diff --git a/benchtests/bench-memset-zerofill.c b/benchtests/bench-memset-zerofill.c
> > > new file mode 100644
> > > index 000000000000..7aa7fe048574
> > > --- /dev/null
> > > +++ b/benchtests/bench-memset-zerofill.c
> > > @@ -0,0 +1,134 @@
> > > +/* Measure memset functions with zero fill data.
> > > +   Copyright (C) 2021 Free Software Foundation, Inc.
> > > +   This file is part of the GNU C Library.
> > > +
> > > +   The GNU C Library is free software; you can redistribute it and/or
> > > +   modify it under the terms of the GNU Lesser General Public
> > > +   License as published by the Free Software Foundation; either
> > > +   version 2.1 of the License, or (at your option) any later version.
> > > +
> > > +   The GNU C Library is distributed in the hope that it will be useful,
> > > +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> > > +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> > > +   Lesser General Public License for more details.
> > > +
> > > +   You should have received a copy of the GNU Lesser General Public
> > > +   License along with the GNU C Library; if not, see
> > > +   <https://www.gnu.org/licenses/>.  */
> > > +
> > > +#define TEST_MAIN
> > > +#define TEST_NAME "memset"
> > > +#define START_SIZE 256
> > > +#define MIN_PAGE_SIZE (getpagesize () + 64 * 1024 * 1024)
> > > +#define TIMEOUT (20 * 60)
> > > +#include "bench-string.h"
> > > +
> > > +#include "json-lib.h"
> > > +
> > > +void *generic_memset (void *, int, size_t);
> > > +typedef void *(*proto_t) (void *, int, size_t);
> > > +
> > > +IMPL (MEMSET, 1)
> > > +IMPL (generic_memset, 0)
> > > +
> > > +static void
> > > +__attribute__((noinline, noclone))
> > > +do_one_test (json_ctx_t *json_ctx, impl_t *impl, CHAR *s,
> > > +            int c1 __attribute ((unused)), int c2 __attribute ((unused)),
> > > +            size_t n)
> > > +{
> > > +  size_t i, iters = 32;
> > > +  timing_t start, stop, cur, latency = 0;
> > > +
> > > +  CALL (impl, s, c2, n); // warm up
> > > +
> > > +  for (i = 0; i < iters; i++)
> > > +    {
> > > +      memset (s, c1, n); // alternation
> > > +
> > > +      TIMING_NOW (start);
> > > +
> > > +      CALL (impl, s, c2, n);
> > > +
> > > +      TIMING_NOW (stop);
> > > +      TIMING_DIFF (cur, start, stop);
> > > +      TIMING_ACCUM (latency, cur);
> > > +    }
> > > +
> > > +  json_element_double (json_ctx, (double) latency / (double) iters);
> > > +}
> > > +
Ok.

> > > +static void
> > > +do_test (json_ctx_t *json_ctx, size_t align, int c1, int c2, size_t len)
> > > +{
> > > +  align &= getpagesize () - 1;
> > > +  if ((align + len) * sizeof (CHAR) > page_size)
> > > +    return;
> > > +
> > > +  json_element_object_begin (json_ctx);
> > > +  json_attr_uint (json_ctx, "length", len);
> > > +  json_attr_uint (json_ctx, "alignment", align);
> > > +  json_attr_int (json_ctx, "char1", c1);
> > > +  json_attr_int (json_ctx, "char2", c2);
> > > +  json_array_begin (json_ctx, "timings");
> > > +
> > > +  FOR_EACH_IMPL (impl, 0)
> > > +    {
> > > +      do_one_test (json_ctx, impl, (CHAR *) (buf1) + align, c1, c2, len);
> > > +      alloc_bufs ();
> > > +    }
> > > +
> > > +  json_array_end (json_ctx);
> > > +  json_element_object_end (json_ctx);
> > > +}
Ok.

> > > +
> > > +int
> > > +test_main (void)
> > > +{
> > > +  json_ctx_t json_ctx;
> > > +  size_t i;
> > > +  int c1, c2;
> > > +
> > > +  test_init ();
> > > +
> > > +  json_init (&json_ctx, 0, stdout);
> > > +
> > > +  json_document_begin (&json_ctx);
> > > +  json_attr_string (&json_ctx, "timing_type", TIMING_TYPE);
> > > +
> > > +  json_attr_object_begin (&json_ctx, "functions");
> > > +  json_attr_object_begin (&json_ctx, TEST_NAME);
> > > +  json_attr_string (&json_ctx, "bench-variant", "zerofill");
> > > +
> > > +  json_array_begin (&json_ctx, "ifuncs");
> > > +  FOR_EACH_IMPL (impl, 0)
> > > +    json_element_string (&json_ctx, impl->name);
> > > +  json_array_end (&json_ctx);
> > > +
> > > +  json_array_begin (&json_ctx, "results");
> > > +
> > > +  for (c1 = 0; c1 < 2; c1++)
> > > +    for (c2 = 0; c2 < 2; c2++)
> > > +      for (i = START_SIZE; i <= MIN_PAGE_SIZE; i <<= 1)
> > > +       {
> > > +         do_test (&json_ctx, 0, c1, c2, i);
> > > +         do_test (&json_ctx, 3, c1, c2, i);
> > > +       }
> > > +
> > > +  json_array_end (&json_ctx);
> > > +  json_attr_object_end (&json_ctx);
> > > +  json_attr_object_end (&json_ctx);
> > > +  json_document_end (&json_ctx);
> > > +
> > > +  return ret;
> > > +}
Ok.

> > > +
> > > +#include <support/test-driver.c>
> > > +
> > > +#define libc_hidden_builtin_def(X)
> > > +#define libc_hidden_def(X)
> > > +#define libc_hidden_weak(X)
> > > +#define weak_alias(X,Y)
> > > +#undef MEMSET
> > > +#define MEMSET generic_memset
> > > +#include <string/memset.c>
> > > --
> > > 2.17.1
> > >