Re: [PATCH 1/2] Add random benchmark

[Carlos O'Donell <carlos@redhat.com>]

On 11/28/23 12:35, Wilco Dijkstra wrote:
> 
> Add a simple benchmark to measure the overhead of internal libc locks in
> the random() implementation on both single- and multi-threaded cases.
> 
> ---
> 
> diff --git a/benchtests/Makefile b/benchtests/Makefile
> index e1346bbda125be9fc2b216f9e8be3f2ee7cb0c4d..1415d20e25798871936f3e2b87f8690517239b21 100644
> --- a/benchtests/Makefile
> +++ b/benchtests/Makefile
> @@ -247,6 +247,7 @@ hash-benchset := \
>  stdlib-benchset := \
>    arc4random \
>    strtod \
> +  random-lock \

Fails pre-commit CI.

https://patchwork.sourceware.org/project/glibc/patch/PAWPR08MB8982D7F540068200C32DA70983BCA@PAWPR08MB8982.eurprd08.prod.outlook.com/

This inserts a routine in a non-sorted order in the alpha-sorted list.

lint-makefiles should fail for you?

>    # stdlib-benchset
>  
>  stdio-common-benchset := sprintf
> diff --git a/benchtests/bench-random-lock.c b/benchtests/bench-random-lock.c
> new file mode 100644
> index 0000000000000000000000000000000000000000..ff11f807359c05043366c855751a97a383b1b132
> --- /dev/null
> +++ b/benchtests/bench-random-lock.c
> @@ -0,0 +1,108 @@
> +/* Benchmark internal libc locking functions used in random.
> +   Copyright (C) 2022-2023 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 "random-lock"
> +
> +#include <pthread.h>
> +#include <stdio.h>
> +#include <stdlib.h>
> +#include "bench-timing.h"
> +#include "json-lib.h"
> +
> +/* Modern cores run 20M iterations in about 1 second.  */
> +#define NUM_ITERS 40000000
> +
> +json_ctx_t json_ctx;
> +
> +
> +/* Measure the overhead of __libc_lock_lock and __libc_lock_unlock by
> +   calling random ().  */
> +static void
> +bench_random_lock (size_t iters)
> +{
> +  timing_t start, stop, total;
> +
> +  srandom (0);
> +
> +  /* Warmup to reduce variations due to frequency scaling.  */
> +  for (int i = 0; i < iters / 4; i++)
> +    (void) random ();
> +
> +  TIMING_NOW (start);
> +
> +  for (int i = 0; i < iters; i++)
> +    (void) random ();
> +
> +  TIMING_NOW (stop);
> +
> +  TIMING_DIFF (total, start, stop);
> +
> +  json_element_double (&json_ctx, (double) total / (double) iters);
> +}
> +
> +static void *
> +thread_start (void *p)
> +{
> +  return p;
> +}
> +
> +int
> +do_bench (void)
> +{
> +  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, "random");
> +  json_attr_string (&json_ctx, "bench-variant", "single-threaded");
> +  json_array_begin (&json_ctx, "results");
> +
> +  /* Run benchmark single threaded.  */
> +  bench_random_lock (NUM_ITERS);
> +
> +  json_array_end (&json_ctx);
> +  json_attr_object_end (&json_ctx);
> +
> +  json_attr_object_begin (&json_ctx, "random");
> +  json_attr_string (&json_ctx, "bench-variant", "multi-threaded");
> +  json_array_begin (&json_ctx, "results");
> +
> +  /* Start a short thread to force SINGLE_THREAD_P == false.  This relies on
> +     the runtime disabling single-threaded optimizations when multiple
> +     threads are used, even after they finish.  */
> +
> +  pthread_t t;
> +  pthread_create (&t, NULL, thread_start, NULL);
> +  pthread_join (t, NULL);
> +
> +  /* Repeat benchmark with single-threaded optimizations disabled.  */
> +  bench_random_lock (NUM_ITERS);
> +
> +  json_array_end (&json_ctx);
> +  json_attr_object_end (&json_ctx);
> +  json_attr_object_end (&json_ctx);
> +  json_document_end (&json_ctx);
> +  return 0;
> +}
> +
> +#define TEST_FUNCTION do_bench ()
> +
> +#include "../test-skeleton.c"
> 
> 
> 

-- 
Cheers,
Carlos.