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0997c3d0c8
Add a simple benchmark to measure the overhead of internal libc locks in the random() implementation on both single- and multi-threaded cases. This relies on the implementation of random using internal locks to access shared global data, and that the runtime uses multi-threaded locking once a thread has been created (even after it finishes). Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
107 lines
3.0 KiB
C
107 lines
3.0 KiB
C
/* Benchmark internal libc locking functions used in random.
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Copyright (C) 2022-2024 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<https://www.gnu.org/licenses/>. */
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#define TEST_MAIN
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#define TEST_NAME "random-lock"
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#define TEST_FUNCTION test_main
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#include <pthread.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include "bench-timing.h"
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#include "json-lib.h"
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/* Modern cores run 20M iterations in about 1 second. */
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#define NUM_ITERS 50000000
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/* Measure the overhead of __libc_lock_lock and __libc_lock_unlock by
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calling random (). */
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static void
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bench_random_lock (json_ctx_t *json_ctx, size_t iters)
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{
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timing_t start, stop, total;
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srandom (0);
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/* Warmup to reduce variations due to frequency scaling. */
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for (int i = 0; i < iters / 4; i++)
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(void) random ();
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TIMING_NOW (start);
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for (int i = 0; i < iters; i++)
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(void) random ();
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TIMING_NOW (stop);
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TIMING_DIFF (total, start, stop);
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json_element_double (json_ctx, (double) total / (double) iters);
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}
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static void *
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thread_start (void *p)
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{
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return p;
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}
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int
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test_main (void)
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{
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json_ctx_t json_ctx;
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json_init (&json_ctx, 0, stdout);
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json_document_begin (&json_ctx);
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json_attr_string (&json_ctx, "timing_type", TIMING_TYPE);
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json_attr_object_begin (&json_ctx, "functions");
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json_attr_object_begin (&json_ctx, "random");
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json_attr_string (&json_ctx, "bench-variant", "single-threaded");
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json_array_begin (&json_ctx, "results");
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/* Run benchmark single threaded. */
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bench_random_lock (&json_ctx, NUM_ITERS);
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json_array_end (&json_ctx);
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json_attr_object_end (&json_ctx);
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json_attr_object_begin (&json_ctx, "random");
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json_attr_string (&json_ctx, "bench-variant", "multi-threaded");
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json_array_begin (&json_ctx, "results");
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/* Start a short thread to force SINGLE_THREAD_P == false. This relies on
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the runtime disabling single-threaded optimizations when multiple
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threads are used, even after they finish. */
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pthread_t t;
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pthread_create (&t, NULL, thread_start, NULL);
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pthread_join (t, NULL);
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/* Repeat benchmark with single-threaded optimizations disabled. */
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bench_random_lock (&json_ctx, NUM_ITERS);
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json_array_end (&json_ctx);
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json_attr_object_end (&json_ctx);
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json_attr_object_end (&json_ctx);
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json_document_end (&json_ctx);
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return 0;
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}
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#include "support/test-driver.c"
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