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

    This program is particularly useful to measure the latency of nthread requeues
    without waking up any tasks -- thus mimicking a regular futex_wait.
    An example run:

    $ perf bench futex requeue -r 100 -t 64
    Run summary [PID 151011]: Requeuing 64 threads (from 0x7d15c4 to 0x7d15c8), 1 at a time.

    [Run 1]: Requeued 64 of 64 threads in 0.0400 ms
    [Run 2]: Requeued 64 of 64 threads in 0.0390 ms
    [Run 3]: Requeued 64 of 64 threads in 0.0400 ms
    ...
    [Run 100]: Requeued 64 of 64 threads in 0.0390 ms
    Requeued 64 of 64 threads in 0.0399 ms (+-0.37%)

    Signed-off-by: Davidlohr Bueso <davidlohr@hp.com>
    ---
    tools/perf/Makefile.perf | 1 +
    tools/perf/bench/bench.h | 1 +
    tools/perf/bench/futex-requeue.c | 211 +++++++++++++++++++++++++++++++++++++++
    tools/perf/bench/futex.h | 13 +++
    tools/perf/builtin-bench.c | 1 +
    5 files changed, 227 insertions(+)
    create mode 100644 tools/perf/bench/futex-requeue.c

    diff --git a/tools/perf/Makefile.perf b/tools/perf/Makefile.perf
    index f2e3536..9dd2c19 100644
    --- a/tools/perf/Makefile.perf
    +++ b/tools/perf/Makefile.perf
    @@ -418,6 +418,7 @@ 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)bench/futex-requeue.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 6ac3f1d..eba4670 100644
    --- a/tools/perf/bench/bench.h
    +++ b/tools/perf/bench/bench.h
    @@ -33,6 +33,7 @@ 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_requeue(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-requeue.c b/tools/perf/bench/futex-requeue.c
    new file mode 100644
    index 0000000..a1625587
    --- /dev/null
    +++ b/tools/perf/bench/futex-requeue.c
    @@ -0,0 +1,211 @@
    +/*
    + * Copyright (C) 2013 Davidlohr Bueso <davidlohr@hp.com>
    + *
    + * futex-requeue: Block a bunch of threads on futex1 and requeue them
    + * on futex2, N at a time.
    + *
    + * This program is particularly useful to measure the latency of nthread
    + * requeues without waking up any tasks -- thus mimicking a regular futex_wait.
    + */
    +
    +#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>
    +
    +static u_int32_t futex1 = 0, futex2 = 0;
    +
    +/*
    + * How many tasks to requeue at a time.
    + * Default to 1 in order to make the kernel work more.
    + */
    +static unsigned int nrequeue = 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;
    +
    +static 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 requeuetime_stats, requeued_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('q', "nrequeue", &nrequeue, "Specify amount of threads to requeue 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_requeue_usage[] = {
    + "perf bench futex requeue <options>",
    + NULL
    +};
    +
    +static void print_summary(void)
    +{
    + double requeuetime_avg = avg_stats(&requeuetime_stats);
    + double requeuetime_stddev = stddev_stats(&requeuetime_stats);
    + unsigned int requeued_avg = avg_stats(&requeued_stats);
    +
    + printf("Requeued %d of %d threads in %.4f ms (+-%.2f%%)\n",
    + requeued_avg,
    + nthreads,
    + requeuetime_avg/1e3,
    + rel_stddev_stats(requeuetime_stddev, requeuetime_avg));
    +}
    +
    +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 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_requeue(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_requeue_usage, 0);
    + if (argc)
    + goto err;
    +
    + 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]: Requeuing %d threads (from %p to %p), "
    + "%d at a time.\n\n",
    + getpid(), nthreads, &futex1, &futex2, nrequeue);
    +
    + init_stats(&requeued_stats);
    + init_stats(&requeuetime_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 nrequeued = 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 requeueing */
    + gettimeofday(&start, NULL);
    + for (nrequeued = 0; nrequeued < nthreads; nrequeued += nrequeue)
    + /*
    + * Do not wakeup any tasks blocked on futex1, allowing
    + * us to really measure futex_wait functionality.
    + */
    + futex_cmp_requeue(&futex1, 0, &futex2, 0, nrequeue,
    + FUTEX_PRIVATE_FLAG);
    + gettimeofday(&end, NULL);
    + timersub(&end, &start, &runtime);
    +
    + update_stats(&requeued_stats, nrequeued);
    + update_stats(&requeuetime_stats, runtime.tv_usec);
    +
    + if (!silent) {
    + printf("[Run %d]: Requeued %d of %d threads in %.4f ms\n",
    + j + 1, nrequeued, nthreads, runtime.tv_usec/1e3);
    + }
    +
    + /* everybody should be blocked on futex2, wake'em up */
    + nrequeued = futex_wake(&futex2, nthreads, FUTEX_PRIVATE_FLAG);
    + if (nthreads != nrequeued)
    + warnx("couldn't wakeup all tasks (%d/%d)", nrequeued, nthreads);
    +
    + 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;
    +err:
    + usage_with_options(bench_futex_requeue_usage, options);
    + exit(EXIT_FAILURE);
    +}
    diff --git a/tools/perf/bench/futex.h b/tools/perf/bench/futex.h
    index 6ac4509..71f2844 100644
    --- a/tools/perf/bench/futex.h
    +++ b/tools/perf/bench/futex.h
    @@ -55,4 +55,17 @@ futex_wake(u_int32_t *uaddr, int nr_wake, int opflags)
    return futex(uaddr, FUTEX_WAKE, nr_wake, NULL, NULL, 0, opflags);
    }

    +/**
    +* futex_cmp_requeue() - requeue tasks from uaddr to uaddr2
    +* @nr_wake: wake up to this many tasks
    +* @nr_requeue: requeue up to this many tasks
    +*/
    +static inline int
    +futex_cmp_requeue(u_int32_t *uaddr, u_int32_t val, u_int32_t *uaddr2, int nr_wake,
    + int nr_requeue, int opflags)
    +{
    + return futex(uaddr, FUTEX_CMP_REQUEUE, nr_wake, nr_requeue, uaddr2,
    + val, opflags);
    +}
    +
    #endif /* _FUTEX_H */
    diff --git a/tools/perf/builtin-bench.c b/tools/perf/builtin-bench.c
    index 743a30a..f600b74 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 },
    + { "requeue", "Benchmark for futex requeue calls", bench_futex_requeue },
    { "all", "Test all futex benchmarks", NULL },
    { NULL, NULL, NULL }
    };
    --
    1.8.1.4


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