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Subject[PATCH 2/3] perf-bench: add futex-wake microbenchmark
Date
Block a bunch of threads on a futex and wake them up, N at a time.

This program is particularly useful to measure the latency of nthread wakeups
in non-error situations: all waiters are queued and all wake calls wakeup
one or more tasks. An example run:

$ perf bench futex -t 512 -r 100
Run summary [PID 27823]: blocking on 512 threads (at futex 0x7e10d4), waking up 1 at a time.

[Run 1]: Wokeup 512 of 512 threads in 6.0080 ms
[Run 2]: Wokeup 512 of 512 threads in 5.2280 ms
[Run 3]: Wokeup 512 of 512 threads in 4.8300 ms
...
[Run 100]: Wokeup 512 of 512 threads in 5.0100 ms
Wokeup 512 of 512 threads in 5.0109 ms (+-2.25%)

Signed-off-by: Davidlohr Bueso <davidlohr@hp.com>
---
tools/perf/Makefile.perf | 1 +
tools/perf/bench/bench.h | 1 +
tools/perf/bench/futex-wake.c | 201 ++++++++++++++++++++++++++++++++++++++++++
tools/perf/bench/futex.h | 10 +++
tools/perf/builtin-bench.c | 1 +
5 files changed, 214 insertions(+)
create mode 100644 tools/perf/bench/futex-wake.c

diff --git a/tools/perf/Makefile.perf b/tools/perf/Makefile.perf
index c38cba4..f2e3536 100644
--- a/tools/perf/Makefile.perf
+++ b/tools/perf/Makefile.perf
@@ -417,6 +417,7 @@ endif
BUILTIN_OBJS += $(OUTPUT)bench/mem-memcpy.o
BUILTIN_OBJS += $(OUTPUT)bench/mem-memset.o
BUILTIN_OBJS += $(OUTPUT)bench/futex-hash.o
+BUILTIN_OBJS += $(OUTPUT)bench/futex-wake.o

BUILTIN_OBJS += $(OUTPUT)builtin-diff.o
BUILTIN_OBJS += $(OUTPUT)builtin-evlist.o
diff --git a/tools/perf/bench/bench.h b/tools/perf/bench/bench.h
index 34edb5c..6ac3f1d 100644
--- a/tools/perf/bench/bench.h
+++ b/tools/perf/bench/bench.h
@@ -32,6 +32,7 @@ extern int bench_mem_memcpy(int argc, const char **argv,
const char *prefix __maybe_unused);
extern int bench_mem_memset(int argc, const char **argv, const char *prefix);
extern int bench_futex_hash(int argc, const char **argv, const char *prefix);
+extern int bench_futex_wake(int argc, const char **argv, const char *prefix);

#define BENCH_FORMAT_DEFAULT_STR "default"
#define BENCH_FORMAT_DEFAULT 0
diff --git a/tools/perf/bench/futex-wake.c b/tools/perf/bench/futex-wake.c
new file mode 100644
index 0000000..d096169
--- /dev/null
+++ b/tools/perf/bench/futex-wake.c
@@ -0,0 +1,201 @@
+/*
+ * Copyright (C) 2013 Davidlohr Bueso <davidlohr@hp.com>
+ *
+ * futex-wake: Block a bunch of threads on a futex and wake'em up, N at a time.
+ *
+ * This program is particularly useful to measure the latency of nthread wakeups
+ * in non-error situations: all waiters are queued and all wake calls wakeup
+ * one or more tasks, and thus the waitqueue is never empty.
+ */
+
+#include "../perf.h"
+#include "../util/util.h"
+#include "../util/stat.h"
+#include "../util/parse-options.h"
+#include "../util/header.h"
+#include "bench.h"
+#include "futex.h"
+
+#include <err.h>
+#include <stdlib.h>
+#include <sys/time.h>
+#include <pthread.h>
+
+/* all threads will block on the same futex */
+static u_int32_t futex1 = 0;
+
+/*
+ * How many wakeups to do at a time.
+ * Default to 1 in order to make the kernel work more.
+ */
+static unsigned int nwakes = 1;
+
+/*
+ * There can be significant variance from run to run,
+ * the more repeats, the more exact the overall avg and
+ * the better idea of the futex latency.
+ */
+static unsigned int repeat = 10;
+
+pthread_t *worker;
+static bool done = 0, silent = 0;
+static pthread_mutex_t thread_lock;
+static pthread_cond_t thread_parent, thread_worker;
+static struct stats waketime_stats, wakeup_stats;
+static unsigned int ncpus, threads_starting, nthreads = 0;
+
+static const struct option options[] = {
+ OPT_UINTEGER('t', "threads", &nthreads, "Specify amount of threads"),
+ OPT_UINTEGER('w', "nwakes", &nwakes, "Specify amount of threads to wake at once"),
+ OPT_UINTEGER('r', "repeat", &repeat, "Specify amount of times to repeat the run"),
+ OPT_BOOLEAN( 's', "silent", &silent, "Silent mode: do not display data/details"),
+ OPT_END()
+};
+
+static const char * const bench_futex_wake_usage[] = {
+ "perf bench futex wake <options>",
+ NULL
+};
+
+static void *workerfn(void *arg __maybe_unused)
+{
+ pthread_mutex_lock(&thread_lock);
+ threads_starting--;
+ if (!threads_starting)
+ pthread_cond_signal(&thread_parent);
+ pthread_cond_wait(&thread_worker, &thread_lock);
+ pthread_mutex_unlock(&thread_lock);
+
+ futex_wait(&futex1, 0, NULL, FUTEX_PRIVATE_FLAG);
+ return NULL;
+}
+
+static void print_summary(void)
+{
+ double waketime_avg = avg_stats(&waketime_stats);
+ double waketime_stddev = stddev_stats(&waketime_stats);
+ unsigned int wakeup_avg = avg_stats(&wakeup_stats);
+
+ printf("Wokeup %d of %d threads in %.4f ms (+-%.2f%%)\n",
+ wakeup_avg,
+ nthreads,
+ waketime_avg/1e3,
+ rel_stddev_stats(waketime_stddev, waketime_avg));
+}
+
+static void block_threads(pthread_t *w,
+ pthread_attr_t thread_attr)
+{
+ cpu_set_t cpu;
+ unsigned int i;
+
+ threads_starting = nthreads;
+
+ /* create and block all threads */
+ for (i = 0; i < nthreads; i++) {
+ CPU_ZERO(&cpu);
+ CPU_SET(i % ncpus, &cpu);
+
+ if (pthread_attr_setaffinity_np(&thread_attr, sizeof(cpu_set_t), &cpu))
+ err(EXIT_FAILURE, "pthread_attr_setaffinity_np");
+
+ if (pthread_create(&w[i], &thread_attr, workerfn, NULL))
+ err(EXIT_FAILURE, "pthread_create");
+ }
+}
+
+static void toggle_done(int sig __maybe_unused,
+ siginfo_t *info __maybe_unused,
+ void *uc __maybe_unused)
+{
+ done = true;
+}
+
+int bench_futex_wake(int argc, const char **argv,
+ const char *prefix __maybe_unused)
+{
+ int ret = 0;
+ unsigned int i, j;
+ struct sigaction act;
+ pthread_attr_t thread_attr;
+
+ argc = parse_options(argc, argv, options, bench_futex_wake_usage, 0);
+ if (argc) {
+ usage_with_options(bench_futex_wake_usage, options);
+ exit(EXIT_FAILURE);
+ }
+
+ ncpus = sysconf(_SC_NPROCESSORS_ONLN);
+
+ sigfillset(&act.sa_mask);
+ act.sa_sigaction = toggle_done;
+ sigaction(SIGINT, &act, NULL);
+
+ if (!nthreads)
+ nthreads = ncpus;
+
+ worker = calloc(nthreads, sizeof(*worker));
+ if (!worker)
+ err(EXIT_FAILURE, "calloc");
+
+ printf("Run summary [PID %d]: blocking on %d threads (at futex %p), "
+ "waking up %d at a time.\n\n",
+ getpid(), nthreads, &futex1, nwakes);
+
+ init_stats(&wakeup_stats);
+ init_stats(&waketime_stats);
+ pthread_attr_init(&thread_attr);
+ pthread_mutex_init(&thread_lock, NULL);
+ pthread_cond_init(&thread_parent, NULL);
+ pthread_cond_init(&thread_worker, NULL);
+
+ for (j = 0; j < repeat && !done; j++) {
+ unsigned int nwoken = 0;
+ struct timeval start, end, runtime;
+
+ /* create, launch & block all threads */
+ block_threads(worker, thread_attr);
+
+ /* make sure all threads are already blocked */
+ pthread_mutex_lock(&thread_lock);
+ while (threads_starting)
+ pthread_cond_wait(&thread_parent, &thread_lock);
+ pthread_cond_broadcast(&thread_worker);
+ pthread_mutex_unlock(&thread_lock);
+
+ usleep(100000);
+
+ /* Ok, all threads are patiently blocked, start waking folks up */
+ gettimeofday(&start, NULL);
+ while (nwoken != nthreads)
+ nwoken += futex_wake(&futex1, nwakes, FUTEX_PRIVATE_FLAG);
+ gettimeofday(&end, NULL);
+ timersub(&end, &start, &runtime);
+
+ update_stats(&wakeup_stats, nwoken);
+ update_stats(&waketime_stats, runtime.tv_usec);
+
+ if (!silent) {
+ printf("[Run %d]: Wokeup %d of %d threads in %.4f ms\n",
+ j + 1, nwoken, nthreads, runtime.tv_usec/1e3);
+ }
+
+ for (i = 0; i < nthreads; i++) {
+ ret = pthread_join(worker[i], NULL);
+ if (ret)
+ err(EXIT_FAILURE, "pthread_join");
+ }
+
+ }
+
+ /* cleanup & report results */
+ pthread_cond_destroy(&thread_parent);
+ pthread_cond_destroy(&thread_worker);
+ pthread_mutex_destroy(&thread_lock);
+ pthread_attr_destroy(&thread_attr);
+
+ print_summary();
+
+ free(worker);
+ return ret;
+}
diff --git a/tools/perf/bench/futex.h b/tools/perf/bench/futex.h
index 7d0bda5..6ac4509 100644
--- a/tools/perf/bench/futex.h
+++ b/tools/perf/bench/futex.h
@@ -45,4 +45,14 @@ futex_wait(u_int32_t *uaddr, u_int32_t val, struct timespec *timeout, int opflag
return futex(uaddr, FUTEX_WAIT, val, timeout, NULL, 0, opflags);
}

+/**
+ * futex_wake() - wake one or more tasks blocked on uaddr
+ * @nr_wake: wake up to this many tasks
+ */
+static inline int
+futex_wake(u_int32_t *uaddr, int nr_wake, int opflags)
+{
+ return futex(uaddr, FUTEX_WAKE, nr_wake, NULL, NULL, 0, opflags);
+}
+
#endif /* _FUTEX_H */
diff --git a/tools/perf/builtin-bench.c b/tools/perf/builtin-bench.c
index a8b0138..743a30a 100644
--- a/tools/perf/builtin-bench.c
+++ b/tools/perf/builtin-bench.c
@@ -57,6 +57,7 @@ static struct bench mem_benchmarks[] = {

static struct bench futex_benchmarks[] = {
{ "hash", "Benchmark for futex hash table", bench_futex_hash },
+ { "wake", "Benchmark for futex wake calls", bench_futex_wake },
{ "all", "Test all futex benchmarks", NULL },
{ NULL, NULL, NULL }
};
--
1.8.1.4


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