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Subject[PATCH v3 13/13] perf bench: New microbenchmark for userspace mutex performance
Date
This microbenchmark simulates how the use of different futex types
can affect the actual performanace of userspace mutex locks. The
usage is:

perf bench futex mutex <options>

Three sets of simple mutex lock and unlock functions are implemented
using the wait-wake, PI and TP futexes respectively. This
microbenchmark then runs the locking rate measurement tests using
either one of those mutexes or all of them consecutively.

Signed-off-by: Waiman Long <Waiman.Long@hpe.com>
---
tools/perf/bench/Build | 1 +
tools/perf/bench/bench.h | 1 +
tools/perf/bench/futex-mutex.c | 558 ++++++++++++++++++++++++++++++++++++++++
tools/perf/bench/futex.h | 25 ++
tools/perf/builtin-bench.c | 4 +
5 files changed, 589 insertions(+), 0 deletions(-)
create mode 100644 tools/perf/bench/futex-mutex.c

diff --git a/tools/perf/bench/Build b/tools/perf/bench/Build
index 60bf119..dc6dfc1 100644
--- a/tools/perf/bench/Build
+++ b/tools/perf/bench/Build
@@ -6,6 +6,7 @@ perf-y += futex-wake.o
perf-y += futex-wake-parallel.o
perf-y += futex-requeue.o
perf-y += futex-lock-pi.o
+perf-y += futex-mutex.o

perf-$(CONFIG_X86_64) += mem-memcpy-x86-64-asm.o
perf-$(CONFIG_X86_64) += mem-memset-x86-64-asm.o
diff --git a/tools/perf/bench/bench.h b/tools/perf/bench/bench.h
index 579a592..b0632df 100644
--- a/tools/perf/bench/bench.h
+++ b/tools/perf/bench/bench.h
@@ -36,6 +36,7 @@ int bench_futex_wake_parallel(int argc, const char **argv, const char *prefix);
int bench_futex_requeue(int argc, const char **argv, const char *prefix);
/* pi futexes */
int bench_futex_lock_pi(int argc, const char **argv, const char *prefix);
+int bench_futex_mutex(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-mutex.c b/tools/perf/bench/futex-mutex.c
new file mode 100644
index 0000000..d48e198
--- /dev/null
+++ b/tools/perf/bench/futex-mutex.c
@@ -0,0 +1,558 @@
+/*
+ * Copyright (C) 2016 Waiman Long
+ *
+ * This microbenchmark simulates how the use of different futex types can
+ * affect the actual performanace of userspace locking primitives like mutex.
+ *
+ * The raw throughput of the futex lock and unlock calls is not a good
+ * indication of actual throughput of the mutex code as it may not really
+ * need to call into the kernel. Therefore, 3 simple mutex lock and unlock
+ * functions are written to implenment a mutex lock using the wait-wake,
+ * PI and TP futexes respectively. These functions serve as the basis for
+ * measuring the locking throughput.
+ */
+
+#include <pthread.h>
+
+#include <signal.h>
+#include <string.h>
+#include "../util/stat.h"
+#include "../perf-sys.h"
+#include <subcmd/parse-options.h>
+#include <linux/compiler.h>
+#include <linux/kernel.h>
+#include <errno.h>
+#include "bench.h"
+#include "futex.h"
+
+#include <err.h>
+#include <stdlib.h>
+#include <sys/time.h>
+
+#define gettid() syscall(SYS_gettid)
+#define __cacheline_aligned __attribute__((__aligned__(64)))
+
+typedef u32 futex_t;
+typedef void (*mutex_lock_fn_t)(futex_t *futex, int tid);
+typedef void (*mutex_unlock_fn_t)(futex_t *futex, int tid);
+
+
+struct worker {
+ futex_t *futex;
+ pthread_t thread;
+
+ /*
+ * Per-thread operation statistics
+ */
+ unsigned int ops; /* # of locking operations */
+ unsigned int locks; /* # of lock futex calls */
+ unsigned int unlocks; /* # of unlock futex calls */
+ unsigned int eagains; /* # of EAGAIN errors */
+ unsigned int lockerrs; /* # of other lock errors */
+ unsigned int unlockerrs;/* # of unlock errors */
+ unsigned int wakeups; /* # of wakeups (unlock return) */
+ unsigned int handoffs; /* # of lock handoff (TP only) */
+ unsigned int steals; /* # of lock steals (TP only) */
+} __cacheline_aligned;
+
+/*
+ * Global cache-aligned futex
+ */
+static futex_t global_futex __cacheline_aligned;
+
+static __thread futex_t thread_id; /* Thread ID */
+static __thread int counter; /* Sleep counter */
+
+static struct worker *worker;
+static unsigned int nsecs = 10;
+static bool verbose, done, fshared, exit_now;
+static unsigned int ncpus, nthreads;
+static int futex_flag;
+static const char *ftype = "all";
+static int csload = 1;
+static int wratio;
+struct timeval start, end, runtime;
+static unsigned int worker_start;
+static unsigned int threads_starting;
+static struct stats throughput_stats;
+static mutex_lock_fn_t mutex_lock_fn;
+static mutex_unlock_fn_t mutex_unlock_fn;
+
+/*
+ * CS - Lock critical section
+ */
+static const struct option options[] = {
+ OPT_STRING ('f', "futex-type", &ftype, "type", "Specify futex type: WW, PI, TP, all (default)"),
+ OPT_INTEGER ('l', "load", &csload, "Specify # of cpu_relax's inside CS, default = 1"),
+ OPT_UINTEGER('t', "threads", &nthreads, "Specify number of threads, default = # of CPUs"),
+ OPT_UINTEGER('r', "runtime", &nsecs, "Specify runtime (in seconds, default = 10s)"),
+ OPT_BOOLEAN ('S', "shared", &fshared, "Use shared futexes instead of private ones"),
+ OPT_BOOLEAN ('v', "verbose", &verbose, "Verbose mode: display thread-level details"),
+ OPT_INTEGER ('w', "wait-ratio", &wratio, "Specify <n>/1024 of CS is 1us sleep, default = 0"),
+ OPT_END()
+};
+
+static const char * const bench_futex_mutex_usage[] = {
+ "perf bench futex mutex <options>",
+ NULL
+};
+
+/**
+ * futex_cmpxchg() - atomic compare and exchange
+ * @uaddr: The address of the futex to be modified
+ * @oldval: The expected value of the futex
+ * @newval: The new value to try and assign the futex
+ *
+ * Implement cmpxchg using gcc atomic builtins.
+ *
+ * Return: the old futex value.
+ */
+static inline futex_t futex_cmpxchg(futex_t *uaddr, futex_t old, futex_t new)
+{
+ return __sync_val_compare_and_swap(uaddr, old, new);
+}
+
+/**
+ * atomic_dec_return - atomically decrement & return the new value
+ * @uaddr: The address of the futex to be decremented
+ * Return: The new value
+ */
+static inline int atomic_dec_return(futex_t *uaddr)
+{
+ return __sync_sub_and_fetch(uaddr, 1);
+}
+
+/**
+ * atomic_inc_return - atomically increment & return the new value
+ * @uaddr: The address of the futex to be incremented
+ * Return: The new value
+ */
+static inline int atomic_inc_return(futex_t *uaddr)
+{
+ return __sync_add_and_fetch(uaddr, 1);
+}
+
+/*
+ * Wait-wake futex lock/unlock functions
+ * futex value: 0 - unlocked
+ * 1 - locked
+ * 2 - locked with waiters (contended)
+ */
+static void ww_mutex_lock(futex_t *futex, int tid)
+{
+ futex_t old, val = *futex;
+ int ret;
+
+ for (;;) {
+ if (!val) {
+ val = futex_cmpxchg(futex, 0, 1);
+ if (val == 0)
+ return;
+ }
+ if (val != 2) {
+ /*
+ * Force value to 2 to indicate waiter
+ */
+ old = val;
+ val = futex_cmpxchg(futex, old, 2);
+ if (val == old)
+ val = 2;
+ else
+ continue;
+ }
+ break;
+ }
+
+ for (;;) {
+ ret = futex_wait(futex, 2, NULL, futex_flag);
+ worker[tid].locks++;
+ if (ret < 0) {
+ if (errno == EAGAIN)
+ worker[tid].eagains++;
+ else
+ worker[tid].lockerrs++;
+ }
+
+ val = *futex;
+ if (val == 2)
+ continue;
+ for (;;) {
+ old = val;
+ val = futex_cmpxchg(futex, old, 2);
+ if (old == val)
+ break;
+ }
+ if (val == 0)
+ break; /* We got the lock */
+ }
+}
+
+static void ww_mutex_unlock(futex_t *futex, int tid)
+{
+ futex_t old, val;
+ int ret;
+
+ val = *futex;
+ do {
+ old = val;
+ val = futex_cmpxchg(futex, old, 0);
+ } while (val != old);
+
+ switch (val) {
+ default:
+ case 1: /* No waiter */
+ break;
+
+ case 2:
+ worker[tid].unlocks++;
+ ret = futex_wake(futex, 1, futex_flag);
+ if (ret < 0)
+ worker[tid].unlockerrs++;
+ else
+ worker[tid].wakeups += ret;
+ break;
+ }
+}
+
+/*
+ * PI futex lock/unlock functions
+ */
+static void pi_mutex_lock(futex_t *futex, int tid)
+{
+ futex_t val;
+ int ret;
+
+ val = futex_cmpxchg(futex, 0, thread_id);
+ if (val == 0)
+ return;
+
+ /*
+ * Retry if an error happens
+ */
+ for (;;) {
+ ret = futex_lock_pi(futex, NULL, futex_flag);
+ worker[tid].locks++;
+ if (ret >= 0)
+ break;
+ worker[tid].lockerrs++;
+ }
+}
+
+static void pi_mutex_unlock(futex_t *futex, int tid)
+{
+ futex_t val;
+ int ret;
+
+ val = futex_cmpxchg(futex, thread_id, 0);
+ if (val == thread_id)
+ return;
+
+ ret = futex_unlock_pi(futex, futex_flag);
+ if (ret < 0)
+ worker[tid].unlockerrs++;
+ else
+ worker[tid].wakeups += ret;
+ worker[tid].unlocks++;
+}
+
+/*
+ * TP futex lock/unlock functions
+ */
+static void tp_mutex_lock(futex_t *futex, int tid)
+{
+ futex_t val;
+ int ret;
+
+ val = futex_cmpxchg(futex, 0, thread_id);
+ if (val == 0)
+ return;
+
+ /*
+ * Retry if an error happens
+ */
+ for (;;) {
+ ret = futex_lock(futex, NULL, futex_flag);
+ worker[tid].locks++;
+ if (ret >= 0)
+ break;
+ worker[tid].lockerrs++;
+ }
+ /*
+ * Check locking method
+ */
+ if (!ret)
+ worker[tid].steals++;
+ else if (ret == 2)
+ worker[tid].handoffs++;
+}
+
+static void tp_mutex_unlock(futex_t *futex, int tid)
+{
+ futex_t val;
+ int ret;
+
+ val = futex_cmpxchg(futex, thread_id, 0);
+ if (val == thread_id)
+ return;
+
+ ret = futex_unlock(futex, futex_flag);
+ if (ret < 0)
+ worker[tid].unlockerrs++;
+ else
+ worker[tid].wakeups += ret;
+ worker[tid].unlocks++;
+}
+
+/*
+ * Load function
+ */
+static inline void load(int tid)
+{
+ int n = csload;
+
+ /*
+ * Optionally does a 1us sleep instead if wratio is defined and
+ * is within bound.
+ */
+ if (wratio && (((counter++ + tid) & 0x3ff) < wratio)) {
+ usleep(1);
+ return;
+ }
+
+ while (n-- > 0)
+ cpu_relax();
+}
+
+/****************************************************************************/
+
+static void toggle_done(int sig __maybe_unused,
+ siginfo_t *info __maybe_unused,
+ void *uc __maybe_unused)
+{
+ /* inform all threads that we're done for the day */
+ done = true;
+ gettimeofday(&end, NULL);
+ timersub(&end, &start, &runtime);
+ if (sig)
+ exit_now = true;
+}
+
+static void *workerfn(void *arg)
+{
+ long tid = (long)arg;
+ struct worker *w = &worker[tid];
+ mutex_lock_fn_t lock_fn = mutex_lock_fn;
+ mutex_unlock_fn_t unlock_fn = mutex_unlock_fn;
+
+ thread_id = gettid();
+ counter = 0;
+
+ atomic_dec_return(&threads_starting);
+
+ /*
+ * Busy wait until asked to start
+ */
+ while (!worker_start)
+ cpu_relax();
+
+ do {
+ lock_fn(w->futex, tid);
+ load(tid);
+ unlock_fn(w->futex, tid);
+ w->ops++; /* One more locking operation */
+ cpu_relax();
+ } while (!done);
+
+ return NULL;
+}
+
+static void create_threads(struct worker *w, pthread_attr_t *thread_attr,
+ long tid)
+{
+ cpu_set_t cpu;
+
+ /*
+ * Bind each thread to a CPU
+ */
+ CPU_ZERO(&cpu);
+ CPU_SET(tid % ncpus, &cpu);
+ w->futex = &global_futex;
+
+ if (pthread_attr_setaffinity_np(thread_attr, sizeof(cpu_set_t), &cpu))
+ err(EXIT_FAILURE, "pthread_attr_setaffinity_np");
+
+ if (pthread_create(&w->thread, thread_attr, workerfn, (void *)tid))
+ err(EXIT_FAILURE, "pthread_create");
+}
+
+static void futex_mutex_test(const char *futex_type)
+{
+ u64 us;
+ unsigned int i;
+ struct worker total;
+ double avg, stddev;
+ pthread_attr_t thread_attr;
+
+ if (exit_now)
+ return;
+
+ if (!strcasecmp(futex_type, "WW")) {
+ futex_type = "WW";
+ mutex_lock_fn = ww_mutex_lock;
+ mutex_unlock_fn = ww_mutex_unlock;
+ } else if (!strcasecmp(futex_type, "PI")) {
+ futex_type = "PI";
+ mutex_lock_fn = pi_mutex_lock;
+ mutex_unlock_fn = pi_mutex_unlock;
+ } else if (!strcasecmp(futex_type, "TP")) {
+ futex_type = "TP";
+ mutex_lock_fn = tp_mutex_lock;
+ mutex_unlock_fn = tp_mutex_unlock;
+
+ /*
+ * Check if TP futex is supported.
+ */
+ futex_unlock(&global_futex, 0);
+ if (errno == ENOSYS) {
+ fprintf(stderr, "\nTP futexes are not supported by the kernel!\n");
+ return;
+ }
+ } else {
+ fprintf(stderr, "Unknown futex type '%s'!\n", futex_type);
+ exit(1);
+ }
+
+ printf("\n=====================================\n");
+ printf("Run summary [PID %d]: %d threads doing %s futex lockings for %d secs.\n\n",
+ getpid(), nthreads, futex_type, nsecs);
+
+ init_stats(&throughput_stats);
+
+ global_futex = 0;
+ done = false;
+ threads_starting = nthreads;
+ pthread_attr_init(&thread_attr);
+
+ for (i = 0; i < nthreads; i++)
+ create_threads(&worker[i], &thread_attr, i);
+ pthread_attr_destroy(&thread_attr);
+
+ while (threads_starting)
+ usleep(1);
+
+ gettimeofday(&start, NULL);
+
+ /*
+ * Start the test
+ *
+ * Unlike the other futex benchmarks, this one uses busy waiting
+ * instead of pthread APIs to make sure that all the threads (except
+ * the one that shares CPU with the parent) will start more or less
+ * simultaineously.
+ */
+ atomic_inc_return(&worker_start);
+ sleep(nsecs);
+ toggle_done(0, NULL, NULL);
+
+ for (i = 0; i < nthreads; i++) {
+ int ret = pthread_join(worker[i].thread, NULL);
+
+ if (ret)
+ err(EXIT_FAILURE, "pthread_join");
+ }
+
+ us = runtime.tv_sec * 1000000 + runtime.tv_usec;
+ memset(&total, 0, sizeof(total));
+ for (i = 0; i < nthreads; i++) {
+ /*
+ * Get a rounded estimate of the # of locking ops/sec.
+ */
+ u64 tp = ((u64)worker[i].ops) * 1000000 / us;
+
+ total.ops += worker[i].ops;
+ total.locks += worker[i].locks;
+ total.unlocks += worker[i].unlocks;
+ total.wakeups += worker[i].wakeups;
+ total.eagains += worker[i].eagains;
+ total.lockerrs += worker[i].lockerrs;
+ total.unlockerrs += worker[i].unlockerrs;
+ total.handoffs += worker[i].handoffs;
+ total.steals += worker[i].steals;
+
+ update_stats(&throughput_stats, tp);
+ if (verbose)
+ printf("[thread %3d] futex: %p [ %ld ops/sec ]\n",
+ i, worker[i].futex, (long)tp);
+ }
+
+ avg = avg_stats(&throughput_stats);
+ stddev = stddev_stats(&throughput_stats);
+
+ printf("Locking statistics:\n");
+ printf("Test run time = %'.2f s\n", (double)us/1000000);
+ printf("Total locking ops = %'d\n", total.ops);
+ printf("Lock futex calls = %'d (%.1f%%)\n", total.locks,
+ (double)total.locks*100/total.ops);
+ printf("Unlock futex calls = %'d (%.1f%%)\n", total.unlocks,
+ (double)total.unlocks*100/total.ops);
+ if (total.wakeups)
+ printf("Process wakeups = %'d\n", total.wakeups);
+ if (total.eagains)
+ printf("EAGAIN lock errors = %'d\n", total.eagains);
+ if (total.lockerrs)
+ printf("Other lock errors = %'d\n", total.lockerrs);
+ if (total.unlockerrs)
+ printf("Unlock errors = %'d\n", total.unlockerrs);
+ if (total.handoffs)
+ printf("Lock handoffs = %'d\n", total.handoffs);
+ if (total.steals)
+ printf("Lock stealings = %'d\n", total.steals);
+
+ printf("\nPer-thread Locking Rates:\n");
+ printf("Avg = %'d ops/sec (+- %.2f%%)\n", (int)(avg + 0.5),
+ rel_stddev_stats(stddev, avg));
+ printf("Min = %'d ops/sec\n", (int)throughput_stats.min);
+ printf("Max = %'d ops/sec\n", (int)throughput_stats.max);
+
+ /* Clear the workers area */
+ memset(worker, 0, sizeof(*worker) * nthreads);
+}
+
+int bench_futex_mutex(int argc, const char **argv,
+ const char *prefix __maybe_unused)
+{
+ struct sigaction act;
+
+ argc = parse_options(argc, argv, options, bench_futex_mutex_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");
+
+ if (!fshared)
+ futex_flag = FUTEX_PRIVATE_FLAG;
+
+ if (!strcmp(ftype, "all")) {
+ futex_mutex_test("WW");
+ futex_mutex_test("PI");
+ futex_mutex_test("TP");
+ } else {
+ futex_mutex_test(ftype);
+ }
+ free(worker);
+ return 0;
+err:
+ usage_with_options(bench_futex_mutex_usage, options);
+ exit(EXIT_FAILURE);
+}
diff --git a/tools/perf/bench/futex.h b/tools/perf/bench/futex.h
index b2e06d1..bd3f0df 100644
--- a/tools/perf/bench/futex.h
+++ b/tools/perf/bench/futex.h
@@ -86,6 +86,31 @@ futex_cmp_requeue(u_int32_t *uaddr, u_int32_t val, u_int32_t *uaddr2, int nr_wak
val, opflags);
}

+#ifndef FUTEX_LOCK
+#define FUTEX_LOCK 13
+#endif
+#ifndef FUTEX_UNLOCK
+#define FUTEX_UNLOCK 14
+#endif
+
+/**
+ * futex_lock() - lock the TP futex
+ */
+static inline int
+futex_lock(u_int32_t *uaddr, struct timespec *timeout, int opflags)
+{
+ return futex(uaddr, FUTEX_LOCK, 0, timeout, NULL, 0, opflags);
+}
+
+/**
+ * futex_unlock() - unlock the TP futex
+ */
+static inline int
+futex_unlock(u_int32_t *uaddr, int opflags)
+{
+ return futex(uaddr, FUTEX_UNLOCK, 0, NULL, NULL, 0, opflags);
+}
+
#ifndef HAVE_PTHREAD_ATTR_SETAFFINITY_NP
#include <pthread.h>
static inline int pthread_attr_setaffinity_np(pthread_attr_t *attr,
diff --git a/tools/perf/builtin-bench.c b/tools/perf/builtin-bench.c
index a1cddc6..3a3a3af 100644
--- a/tools/perf/builtin-bench.c
+++ b/tools/perf/builtin-bench.c
@@ -20,6 +20,7 @@
#include "builtin.h"
#include "bench/bench.h"

+#include <locale.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
@@ -62,6 +63,7 @@ static struct bench futex_benchmarks[] = {
{ "requeue", "Benchmark for futex requeue calls", bench_futex_requeue },
/* pi-futexes */
{ "lock-pi", "Benchmark for futex lock_pi calls", bench_futex_lock_pi },
+ { "mutex", "Benchmark for mutex locks using futexes", bench_futex_mutex },
{ "all", "Run all futex benchmarks", NULL },
{ NULL, NULL, NULL }
};
@@ -222,6 +224,8 @@ int cmd_bench(int argc, const char **argv, const char *prefix __maybe_unused)
goto end;
}

+ setlocale(LC_NUMERIC, "en_US"); /* Allow better number formatting */
+
argc = parse_options(argc, argv, bench_options, bench_usage,
PARSE_OPT_STOP_AT_NON_OPTION);

--
1.7.1
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