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Subject[PATCH 24/30] perf bench futex: Support parallel waker threads
Date
From: Davidlohr Bueso <dave@stgolabs.net>

The futex-wake benchmark only measures wakeups done within a single
process. While this has value in its own, it does not really generate
any hb->lock contention.

A new benchmark 'wake-parallel' is added, by extending the futex-wake
code such that we can measure parallel waker threads. The program output
shows the avg per-thread latency in order to complete its share of
wakeups:

Run summary [PID 13474]: blocking on 512 threads (at [private] futex 0xa88668), 8 threads waking up 64 at a time.

[Run 1]: Avg per-thread latency (waking 64/512 threads) in 0.6230 ms (+-15.31%)
[Run 2]: Avg per-thread latency (waking 64/512 threads) in 0.5175 ms (+-29.95%)
[Run 3]: Avg per-thread latency (waking 64/512 threads) in 0.7578 ms (+-18.03%)
[Run 4]: Avg per-thread latency (waking 64/512 threads) in 0.8944 ms (+-12.54%)
[Run 5]: Avg per-thread latency (waking 64/512 threads) in 1.1204 ms (+-23.85%)
Avg per-thread latency (waking 64/512 threads) in 0.7826 ms (+-9.91%)

Naturally, different combinations of numbers of blocking and waker
threads will exhibit different information.

Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Davidlohr Bueso <dbueso@suse.de>
Link: http://lkml.kernel.org/r/1431110280-20231-1-git-send-email-dave@stgolabs.net
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
---
tools/perf/Documentation/perf-bench.txt | 3 +
tools/perf/bench/Build | 1 +
tools/perf/bench/bench.h | 2 +
tools/perf/bench/futex-wake-parallel.c | 294 ++++++++++++++++++++++++++++++++
tools/perf/builtin-bench.c | 1 +
5 files changed, 301 insertions(+)
create mode 100644 tools/perf/bench/futex-wake-parallel.c

diff --git a/tools/perf/Documentation/perf-bench.txt b/tools/perf/Documentation/perf-bench.txt
index f6480cb..bf3d064 100644
--- a/tools/perf/Documentation/perf-bench.txt
+++ b/tools/perf/Documentation/perf-bench.txt
@@ -210,6 +210,9 @@ Suite for evaluating hash tables.
*wake*::
Suite for evaluating wake calls.

+*wake-parallel*::
+Suite for evaluating parallel wake calls.
+
*requeue*::
Suite for evaluating requeue calls.

diff --git a/tools/perf/bench/Build b/tools/perf/bench/Build
index 5ce9802..c3ab760 100644
--- a/tools/perf/bench/Build
+++ b/tools/perf/bench/Build
@@ -3,6 +3,7 @@ perf-y += sched-pipe.o
perf-y += mem-memcpy.o
perf-y += futex-hash.o
perf-y += futex-wake.o
+perf-y += futex-wake-parallel.o
perf-y += futex-requeue.o

perf-$(CONFIG_X86_64) += mem-memcpy-x86-64-asm.o
diff --git a/tools/perf/bench/bench.h b/tools/perf/bench/bench.h
index 3c4dd44..70b2f71 100644
--- a/tools/perf/bench/bench.h
+++ b/tools/perf/bench/bench.h
@@ -33,6 +33,8 @@ extern int bench_mem_memcpy(int argc, const char **argv,
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);
+extern int bench_futex_wake_parallel(int argc, const char **argv,
+ const char *prefix);
extern int bench_futex_requeue(int argc, const char **argv, const char *prefix);

#define BENCH_FORMAT_DEFAULT_STR "default"
diff --git a/tools/perf/bench/futex-wake-parallel.c b/tools/perf/bench/futex-wake-parallel.c
new file mode 100644
index 0000000..6d8c9fa
--- /dev/null
+++ b/tools/perf/bench/futex-wake-parallel.c
@@ -0,0 +1,294 @@
+/*
+ * Copyright (C) 2015 Davidlohr Bueso.
+ *
+ * Block a bunch of threads and let parallel waker threads wakeup an
+ * equal amount of them. The program output reflects the avg latency
+ * for each individual thread to service its share of work. Ultimately
+ * it can be used to measure futex_wake() changes.
+ */
+
+#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>
+
+struct thread_data {
+ pthread_t worker;
+ unsigned int nwoken;
+ struct timeval runtime;
+};
+
+static unsigned int nwakes = 1;
+
+/* all threads will block on the same futex -- hash bucket chaos ;) */
+static u_int32_t futex = 0;
+
+static pthread_t *blocked_worker;
+static bool done = false, silent = false, fshared = false;
+static unsigned int nblocked_threads = 0, nwaking_threads = 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;
+static int futex_flag = 0;
+
+static const struct option options[] = {
+ OPT_UINTEGER('t', "threads", &nblocked_threads, "Specify amount of threads"),
+ OPT_UINTEGER('w', "nwakers", &nwaking_threads, "Specify amount of waking threads"),
+ OPT_BOOLEAN( 's', "silent", &silent, "Silent mode: do not display data/details"),
+ OPT_BOOLEAN( 'S', "shared", &fshared, "Use shared futexes instead of private ones"),
+ OPT_END()
+};
+
+static const char * const bench_futex_wake_parallel_usage[] = {
+ "perf bench futex wake-parallel <options>",
+ NULL
+};
+
+static void *waking_workerfn(void *arg)
+{
+ struct thread_data *waker = (struct thread_data *) arg;
+ struct timeval start, end;
+
+ gettimeofday(&start, NULL);
+
+ waker->nwoken = futex_wake(&futex, nwakes, futex_flag);
+ if (waker->nwoken != nwakes)
+ warnx("couldn't wakeup all tasks (%d/%d)",
+ waker->nwoken, nwakes);
+
+ gettimeofday(&end, NULL);
+ timersub(&end, &start, &waker->runtime);
+
+ pthread_exit(NULL);
+ return NULL;
+}
+
+static void wakeup_threads(struct thread_data *td, pthread_attr_t thread_attr)
+{
+ unsigned int i;
+
+ pthread_attr_setdetachstate(&thread_attr, PTHREAD_CREATE_JOINABLE);
+
+ /* create and block all threads */
+ for (i = 0; i < nwaking_threads; i++) {
+ /*
+ * Thread creation order will impact per-thread latency
+ * as it will affect the order to acquire the hb spinlock.
+ * For now let the scheduler decide.
+ */
+ if (pthread_create(&td[i].worker, &thread_attr,
+ waking_workerfn, (void *)&td[i]))
+ err(EXIT_FAILURE, "pthread_create");
+ }
+
+ for (i = 0; i < nwaking_threads; i++)
+ if (pthread_join(td[i].worker, NULL))
+ err(EXIT_FAILURE, "pthread_join");
+}
+
+static void *blocked_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);
+
+ while (1) { /* handle spurious wakeups */
+ if (futex_wait(&futex, 0, NULL, futex_flag) != EINTR)
+ break;
+ }
+
+ pthread_exit(NULL);
+ return NULL;
+}
+
+static void block_threads(pthread_t *w, pthread_attr_t thread_attr)
+{
+ cpu_set_t cpu;
+ unsigned int i;
+
+ threads_starting = nblocked_threads;
+
+ /* create and block all threads */
+ for (i = 0; i < nblocked_threads; 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, blocked_workerfn, NULL))
+ err(EXIT_FAILURE, "pthread_create");
+ }
+}
+
+static void print_run(struct thread_data *waking_worker, unsigned int run_num)
+{
+ unsigned int i, wakeup_avg;
+ double waketime_avg, waketime_stddev;
+ struct stats __waketime_stats, __wakeup_stats;
+
+ init_stats(&__wakeup_stats);
+ init_stats(&__waketime_stats);
+
+ for (i = 0; i < nwaking_threads; i++) {
+ update_stats(&__waketime_stats, waking_worker[i].runtime.tv_usec);
+ update_stats(&__wakeup_stats, waking_worker[i].nwoken);
+ }
+
+ waketime_avg = avg_stats(&__waketime_stats);
+ waketime_stddev = stddev_stats(&__waketime_stats);
+ wakeup_avg = avg_stats(&__wakeup_stats);
+
+ printf("[Run %d]: Avg per-thread latency (waking %d/%d threads) "
+ "in %.4f ms (+-%.2f%%)\n", run_num + 1, wakeup_avg,
+ nblocked_threads, waketime_avg/1e3,
+ rel_stddev_stats(waketime_stddev, waketime_avg));
+}
+
+static void print_summary(void)
+{
+ unsigned int wakeup_avg;
+ double waketime_avg, waketime_stddev;
+
+ waketime_avg = avg_stats(&waketime_stats);
+ waketime_stddev = stddev_stats(&waketime_stats);
+ wakeup_avg = avg_stats(&wakeup_stats);
+
+ printf("Avg per-thread latency (waking %d/%d threads) in %.4f ms (+-%.2f%%)\n",
+ wakeup_avg,
+ nblocked_threads,
+ waketime_avg/1e3,
+ rel_stddev_stats(waketime_stddev, waketime_avg));
+}
+
+
+static void do_run_stats(struct thread_data *waking_worker)
+{
+ unsigned int i;
+
+ for (i = 0; i < nwaking_threads; i++) {
+ update_stats(&waketime_stats, waking_worker[i].runtime.tv_usec);
+ update_stats(&wakeup_stats, waking_worker[i].nwoken);
+ }
+
+}
+
+static void toggle_done(int sig __maybe_unused,
+ siginfo_t *info __maybe_unused,
+ void *uc __maybe_unused)
+{
+ done = true;
+}
+
+int bench_futex_wake_parallel(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;
+ struct thread_data *waking_worker;
+
+ argc = parse_options(argc, argv, options,
+ bench_futex_wake_parallel_usage, 0);
+ if (argc) {
+ usage_with_options(bench_futex_wake_parallel_usage, options);
+ exit(EXIT_FAILURE);
+ }
+
+ sigfillset(&act.sa_mask);
+ act.sa_sigaction = toggle_done;
+ sigaction(SIGINT, &act, NULL);
+
+ ncpus = sysconf(_SC_NPROCESSORS_ONLN);
+ if (!nblocked_threads)
+ nblocked_threads = ncpus;
+
+ /* some sanity checks */
+ if (nwaking_threads > nblocked_threads || !nwaking_threads)
+ nwaking_threads = nblocked_threads;
+
+ if (nblocked_threads % nwaking_threads)
+ errx(EXIT_FAILURE, "Must be perfectly divisible");
+ /*
+ * Each thread will wakeup nwakes tasks in
+ * a single futex_wait call.
+ */
+ nwakes = nblocked_threads/nwaking_threads;
+
+ blocked_worker = calloc(nblocked_threads, sizeof(*blocked_worker));
+ if (!blocked_worker)
+ err(EXIT_FAILURE, "calloc");
+
+ if (!fshared)
+ futex_flag = FUTEX_PRIVATE_FLAG;
+
+ printf("Run summary [PID %d]: blocking on %d threads (at [%s] "
+ "futex %p), %d threads waking up %d at a time.\n\n",
+ getpid(), nblocked_threads, fshared ? "shared":"private",
+ &futex, nwaking_threads, 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 < bench_repeat && !done; j++) {
+ waking_worker = calloc(nwaking_threads, sizeof(*waking_worker));
+ if (!waking_worker)
+ err(EXIT_FAILURE, "calloc");
+
+ /* create, launch & block all threads */
+ block_threads(blocked_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 */
+ wakeup_threads(waking_worker, thread_attr);
+
+ for (i = 0; i < nblocked_threads; i++) {
+ ret = pthread_join(blocked_worker[i], NULL);
+ if (ret)
+ err(EXIT_FAILURE, "pthread_join");
+ }
+
+ do_run_stats(waking_worker);
+ if (!silent)
+ print_run(waking_worker, j);
+
+ free(waking_worker);
+ }
+
+ /* 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(blocked_worker);
+ return ret;
+}
diff --git a/tools/perf/builtin-bench.c b/tools/perf/builtin-bench.c
index b9a56fa..b5314e4 100644
--- a/tools/perf/builtin-bench.c
+++ b/tools/perf/builtin-bench.c
@@ -58,6 +58,7 @@ 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 },
+ { "wake-parallel", "Benchmark for parallel futex wake calls", bench_futex_wake_parallel },
{ "requeue", "Benchmark for futex requeue calls", bench_futex_requeue },
{ "all", "Test all futex benchmarks", NULL },
{ NULL, NULL, NULL }
--
2.1.0


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