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554 lines
13 KiB
C
554 lines
13 KiB
C
/* Measure various lock acquisition times for empty critical sections.
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Copyright (C) 2020-2023 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 "pthread-locks"
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#include <stdio.h>
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#include <string.h>
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#include <limits.h>
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#include <stdlib.h>
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#include <pthread.h>
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#include <semaphore.h>
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#include <stdatomic.h>
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#include <sys/time.h>
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#include <math.h>
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#include "bench-timing.h"
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#include "json-lib.h"
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/* The point of this benchmark is to measure the overhead of an empty
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critical section or a small critical section. This is never going
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to be indicative of real application performance. Instead we are
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trying to benchmark the effects of the compiler and the runtime
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coupled with a particular set of hardware atomic operations.
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The numbers from this benchmark should be taken with a massive gain
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of salt and viewed through the eyes of expert reviewers. */
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static pthread_mutex_t m;
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static pthread_rwlock_t rw;
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static pthread_cond_t cv;
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static pthread_cond_t consumer_c, producer_c;
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static int cv_done;
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static pthread_spinlock_t sp;
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static sem_t sem;
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typedef timing_t (*test_t)(long, int);
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#define START_ITERS 1000
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#define FILLER_GOES_HERE \
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if (filler) \
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do_filler ();
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/* Everyone loves a good fibonacci series. This isn't quite one of
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them because we need larger values in fewer steps, in a way that
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won't be optimized away. We're looking to approximately double the
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total time each test iteration takes, so as to not swamp the useful
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timings. */
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#pragma GCC push_options
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#pragma GCC optimize(1)
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static int __attribute__((noinline))
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fibonacci (int i)
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{
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asm("");
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if (i > 2)
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return fibonacci (i-1) + fibonacci (i-2);
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return 10+i;
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}
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static void
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do_filler (void)
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{
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static char buf1[512], buf2[512];
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int f = fibonacci (5);
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memcpy (buf1, buf2, f);
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}
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#pragma GCC pop_options
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static timing_t
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test_mutex (long iters, int filler)
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{
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timing_t start, stop, cur;
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pthread_mutex_init (&m, NULL);
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TIMING_NOW (start);
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for (long j = iters; j >= 0; --j)
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{
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pthread_mutex_lock (&m);
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FILLER_GOES_HERE;
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pthread_mutex_unlock (&m);
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}
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TIMING_NOW (stop);
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TIMING_DIFF (cur, start, stop);
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return cur;
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}
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static timing_t
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test_mutex_trylock (long iters, int filler)
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{
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timing_t start, stop, cur;
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pthread_mutex_init (&m, NULL);
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pthread_mutex_lock (&m);
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TIMING_NOW (start);
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for (long j = iters; j >= 0; --j)
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{
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pthread_mutex_trylock (&m);
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FILLER_GOES_HERE;
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}
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TIMING_NOW (stop);
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TIMING_DIFF (cur, start, stop);
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pthread_mutex_unlock (&m);
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return cur;
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}
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static timing_t
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test_rwlock_read (long iters, int filler)
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{
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timing_t start, stop, cur;
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pthread_rwlock_init (&rw, NULL);
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TIMING_NOW (start);
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for (long j = iters; j >= 0; --j)
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{
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pthread_rwlock_rdlock (&rw);
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FILLER_GOES_HERE;
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pthread_rwlock_unlock (&rw);
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}
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TIMING_NOW (stop);
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TIMING_DIFF (cur, start, stop);
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return cur;
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}
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static timing_t
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test_rwlock_tryread (long iters, int filler)
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{
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timing_t start, stop, cur;
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pthread_rwlock_init (&rw, NULL);
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pthread_rwlock_wrlock (&rw);
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TIMING_NOW (start);
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for (long j = iters; j >= 0; --j)
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{
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pthread_rwlock_tryrdlock (&rw);
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FILLER_GOES_HERE;
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}
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TIMING_NOW (stop);
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TIMING_DIFF (cur, start, stop);
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pthread_rwlock_unlock (&rw);
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return cur;
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}
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static timing_t
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test_rwlock_write (long iters, int filler)
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{
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timing_t start, stop, cur;
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pthread_rwlock_init (&rw, NULL);
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TIMING_NOW (start);
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for (long j = iters; j >= 0; --j)
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{
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pthread_rwlock_wrlock (&rw);
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FILLER_GOES_HERE;
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pthread_rwlock_unlock (&rw);
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}
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TIMING_NOW (stop);
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TIMING_DIFF (cur, start, stop);
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return cur;
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}
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static timing_t
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test_rwlock_trywrite (long iters, int filler)
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{
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timing_t start, stop, cur;
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pthread_rwlock_init (&rw, NULL);
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pthread_rwlock_rdlock (&rw);
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TIMING_NOW (start);
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for (long j = iters; j >= 0; --j)
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{
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pthread_rwlock_trywrlock (&rw);
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FILLER_GOES_HERE;
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}
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TIMING_NOW (stop);
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TIMING_DIFF (cur, start, stop);
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pthread_rwlock_unlock (&rw);
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return cur;
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}
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static timing_t
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test_spin_lock (long iters, int filler)
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{
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timing_t start, stop, cur;
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pthread_spin_init (&sp, PTHREAD_PROCESS_PRIVATE);
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TIMING_NOW (start);
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for (long j = iters; j >= 0; --j)
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{
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pthread_spin_lock (&sp);
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FILLER_GOES_HERE;
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pthread_spin_unlock (&sp);
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}
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TIMING_NOW (stop);
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TIMING_DIFF (cur, start, stop);
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return cur;
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}
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static timing_t
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test_spin_trylock (long iters, int filler)
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{
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timing_t start, stop, cur;
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pthread_spin_init (&sp, PTHREAD_PROCESS_PRIVATE);
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pthread_spin_lock (&sp);
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TIMING_NOW (start);
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for (long j = iters; j >= 0; --j)
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{
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pthread_spin_trylock (&sp);
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FILLER_GOES_HERE;
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}
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TIMING_NOW (stop);
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TIMING_DIFF (cur, start, stop);
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pthread_spin_unlock (&sp);
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return cur;
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}
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static timing_t
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test_sem_wait (long iters, int filler)
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{
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timing_t start, stop, cur;
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sem_init (&sem, 0, 1);
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TIMING_NOW (start);
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for (long j = iters; j >= 0; --j)
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{
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sem_post (&sem);
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FILLER_GOES_HERE;
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sem_wait (&sem);
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}
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TIMING_NOW (stop);
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TIMING_DIFF (cur, start, stop);
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return cur;
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}
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static timing_t
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test_sem_trywait (long iters, int filler)
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{
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timing_t start, stop, cur;
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sem_init (&sem, 0, 0);
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TIMING_NOW (start);
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for (long j = iters; j >= 0; --j)
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{
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sem_trywait (&sem);
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FILLER_GOES_HERE;
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}
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TIMING_NOW (stop);
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TIMING_DIFF (cur, start, stop);
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return cur;
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}
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static void *
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test_condvar_helper (void *v)
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{
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/* This is wasteful, but the alternative is to add the overhead of a
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mutex lock/unlock to the overall iteration (both threads) and we
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don't want that. Ideally, this thread would run on an
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independent processing core anyway. The ONLY goal here is to
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minimize the time the other thread spends waiting for us. */
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while (__atomic_load_n (&cv_done, __ATOMIC_RELAXED) == 0)
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pthread_cond_signal (&cv);
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return NULL;
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}
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static timing_t
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test_condvar (long iters, int filler)
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{
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timing_t start, stop, cur;
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pthread_t helper_id;
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pthread_mutex_init (&m, NULL);
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pthread_cond_init (&cv, NULL);
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pthread_mutex_lock (&m);
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__atomic_store_n (&cv_done, 0, __ATOMIC_RELAXED);
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pthread_create (&helper_id, NULL, test_condvar_helper, &iters);
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TIMING_NOW (start);
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for (long j = iters; j >= 0; --j)
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{
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pthread_cond_wait (&cv, &m);
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FILLER_GOES_HERE;
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}
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TIMING_NOW (stop);
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TIMING_DIFF (cur, start, stop);
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pthread_mutex_unlock (&m);
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__atomic_store_n (&cv_done, 1, __ATOMIC_RELAXED);
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pthread_join (helper_id, NULL);
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return cur;
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}
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/* How many items are "queued" in our pretend queue. */
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static int queued = 0;
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typedef struct Producer_Params {
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long iters;
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int filler;
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} Producer_Params;
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/* We only benchmark the consumer thread, but both threads are doing
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essentially the same thing, and never run in parallel due to the
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locks. Thus, even if they run on separate processing cores, we
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count the time for both threads. */
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static void *
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test_producer_thread (void *v)
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{
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Producer_Params *p = (Producer_Params *) v;
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long iters = p->iters;
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int filler = p->filler;
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long j;
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for (j = iters; j >= 0; --j)
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{
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/* Acquire lock on the queue. */
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pthread_mutex_lock (&m);
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/* if something's already there, wait. */
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while (queued > 0)
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pthread_cond_wait (&consumer_c, &m);
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/* Put something on the queue */
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FILLER_GOES_HERE;
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++ queued;
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pthread_cond_signal (&producer_c);
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/* Give the other thread a chance to run. */
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pthread_mutex_unlock (&m);
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}
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return NULL;
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}
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static timing_t
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test_consumer_producer (long iters, int filler)
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{
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timing_t start, stop, cur;
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pthread_t helper_id;
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Producer_Params p;
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p.iters = iters;
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p.filler = filler;
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pthread_mutex_init (&m, NULL);
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pthread_cond_init (&cv, NULL);
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pthread_create (&helper_id, NULL, test_producer_thread, &p);
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TIMING_NOW (start);
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for (long j = iters; j >= 0; --j)
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{
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/* Acquire lock on the queue. */
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pthread_mutex_lock (&m);
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/* Wait for something to be on the queue. */
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while (queued == 0)
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pthread_cond_wait (&producer_c, &m);
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/* Take if off. */
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FILLER_GOES_HERE;
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-- queued;
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pthread_cond_signal (&consumer_c);
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/* Give the other thread a chance to run. */
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pthread_mutex_unlock (&m);
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}
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TIMING_NOW (stop);
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TIMING_DIFF (cur, start, stop);
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pthread_join (helper_id, NULL);
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return cur;
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}
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/* Number of runs we use for computing mean and standard deviation.
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We actually do two additional runs and discard the outliers. */
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#define RUN_COUNT 10
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static int
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do_bench_2 (const char *name, test_t func, int filler, json_ctx_t *js)
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{
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timing_t cur;
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struct timeval ts, te;
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double tsd, ted, td;
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long iters, iters_limit;
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timing_t curs[RUN_COUNT + 2];
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int i, j;
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double mean, stdev;
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iters = START_ITERS;
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iters_limit = LONG_MAX / 100;
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while (1) {
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gettimeofday (&ts, NULL);
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cur = func(iters, filler);
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gettimeofday (&te, NULL);
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/* We want a test to take at least 0.01 seconds, and try
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increasingly larger iteration counts until it does. This
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allows for approximately constant-time tests regardless of
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hardware speed, without the overhead of checking the time
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inside the test loop itself. We stop at a million iterations
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as that should be precise enough. Once we determine a suitable
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iteration count, we run the test multiple times to calculate
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mean and standard deviation. */
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/* Note that this also primes the CPU cache and triggers faster
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MHz, we hope. */
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tsd = ts.tv_sec + ts.tv_usec / 1000000.0;
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ted = te.tv_sec + te.tv_usec / 1000000.0;
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td = ted - tsd;
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if (td >= 0.01
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|| iters >= iters_limit
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|| iters >= 1000000)
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break;
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iters *= 10;
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}
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curs[0] = cur;
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for (i = 1; i < RUN_COUNT + 2; i ++)
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curs[i] = func(iters, filler);
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/* We sort the results so we can discard the fastest and slowest
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times as outliers. In theory we should keep the fastest time,
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but IMHO this is more fair. A simple bubble sort suffices. */
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for (i = 0; i < RUN_COUNT + 1; i ++)
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for (j = i + 1; j < RUN_COUNT + 2; j ++)
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if (curs[i] > curs[j])
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{
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timing_t temp = curs[i];
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curs[i] = curs[j];
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curs[j] = temp;
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}
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/* Now calculate mean and standard deviation, skipping the outliers. */
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mean = 0.0;
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for (i = 1; i<RUN_COUNT + 1; i ++)
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mean += (double) curs[i] / (double) iters;
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mean /= RUN_COUNT;
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stdev = 0.0;
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for (i = 1; i < RUN_COUNT + 1; i ++)
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{
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double s = (double) curs[i] / (double) iters - mean;
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stdev += s * s;
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}
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stdev = sqrt (stdev / (RUN_COUNT - 1));
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char buf[128];
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snprintf (buf, sizeof buf, "%s-%s", name, filler ? "filler" : "empty");
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json_attr_object_begin (js, buf);
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json_attr_double (js, "duration", (double) cur);
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json_attr_double (js, "iterations", (double) iters);
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json_attr_double (js, "wall-sec", (double) td);
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json_attr_double (js, "mean", mean);
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json_attr_double (js, "stdev", stdev);
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json_attr_double (js, "min-outlier", (double) curs[0] / (double) iters);
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json_attr_double (js, "min", (double) curs[1] / (double) iters);
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json_attr_double (js, "max", (double) curs[RUN_COUNT] / (double) iters);
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json_attr_double (js, "max-outlier", (double) curs[RUN_COUNT + 1] / (double) iters);
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json_attr_object_end (js);
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return 0;
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}
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static int
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do_bench_1 (const char *name, test_t func, json_ctx_t *js)
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{
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int rv = 0;
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rv += do_bench_2 (name, func, 0, js);
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rv += do_bench_2 (name, func, 1, js);
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return rv;
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}
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int
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do_bench (void)
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{
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int rv = 0;
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json_ctx_t json_ctx;
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json_init (&json_ctx, 2, stdout);
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json_attr_object_begin (&json_ctx, "pthread_locks");
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#define BENCH(n) rv += do_bench_1 (#n, test_##n, &json_ctx)
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BENCH (mutex);
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BENCH (mutex_trylock);
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BENCH (rwlock_read);
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BENCH (rwlock_tryread);
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BENCH (rwlock_write);
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BENCH (rwlock_trywrite);
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BENCH (spin_lock);
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BENCH (spin_trylock);
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BENCH (sem_wait);
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BENCH (sem_trywait);
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BENCH (condvar);
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BENCH (consumer_producer);
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json_attr_object_end (&json_ctx);
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return rv;
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}
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#define TEST_FUNCTION do_bench ()
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#include "../test-skeleton.c"
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