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