[tip: locking/futex] tools/perf: Allow to select the number of hash buckets

From: tip-bot2 for Sebastian Andrzej Siewior
Date: Thu May 08 2025 - 06:34:35 EST

The following commit has been merged into the locking/futex branch of tip:

Commit-ID: 60035a3981a7f9d965df81a48a07b94e52ccd54f
Gitweb: https://git.kernel.org/tip/60035a3981a7f9d965df81a48a07b94e52ccd54f
Author: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
AuthorDate: Wed, 16 Apr 2025 18:29:19 +02:00
Committer: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Sat, 03 May 2025 12:02:10 +02:00

tools/perf: Allow to select the number of hash buckets

Add the -b/ --buckets argument to specify the number of hash buckets for
the private futex hash. This is directly passed to
prctl(PR_FUTEX_HASH, PR_FUTEX_HASH_SET_SLOTS, buckets, immutable)

and must return without an error if specified. The `immutable' is 0 by
default and can be set to 1 via the -I/ --immutable argument.
The size of the private hash is verified with PR_FUTEX_HASH_GET_SLOTS.
If PR_FUTEX_HASH_GET_SLOTS failed then it is assumed that an older
kernel was used without the support and that the global hash is used.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20250416162921.513656-20-bigeasy@xxxxxxxxxxxxx
---
tools/perf/bench/Build | 1 +-
tools/perf/bench/futex-hash.c | 7 +++-
tools/perf/bench/futex-lock-pi.c | 5 ++-
tools/perf/bench/futex-requeue.c | 6 ++-
tools/perf/bench/futex-wake-parallel.c | 9 ++-
tools/perf/bench/futex-wake.c | 4 ++-
tools/perf/bench/futex.c | 65 +++++++++++++++++++++++++-
tools/perf/bench/futex.h | 5 ++-
8 files changed, 101 insertions(+), 1 deletion(-)
create mode 100644 tools/perf/bench/futex.c

diff --git a/tools/perf/bench/Build b/tools/perf/bench/Build
index 279ab2a..b558ab9 100644
--- a/tools/perf/bench/Build
+++ b/tools/perf/bench/Build
@@ -3,6 +3,7 @@ perf-bench-y += sched-pipe.o
perf-bench-y += sched-seccomp-notify.o
perf-bench-y += syscall.o
perf-bench-y += mem-functions.o
+perf-bench-y += futex.o
perf-bench-y += futex-hash.o
perf-bench-y += futex-wake.o
perf-bench-y += futex-wake-parallel.o
diff --git a/tools/perf/bench/futex-hash.c b/tools/perf/bench/futex-hash.c
index b472ede..fdf133c 100644
--- a/tools/perf/bench/futex-hash.c
+++ b/tools/perf/bench/futex-hash.c
@@ -18,9 +18,11 @@
#include <stdlib.h>
#include <linux/compiler.h>
#include <linux/kernel.h>
+#include <linux/prctl.h>
#include <linux/zalloc.h>
#include <sys/time.h>
#include <sys/mman.h>
+#include <sys/prctl.h>
#include <perf/cpumap.h>

#include "../util/mutex.h"
@@ -50,9 +52,12 @@ struct worker {
static struct bench_futex_parameters params = {
.nfutexes = 1024,
.runtime = 10,
+ .nbuckets = -1,
};

static const struct option options[] = {
+ OPT_INTEGER( 'b', "buckets", &params.nbuckets, "Specify amount of hash buckets"),
+ OPT_BOOLEAN( 'I', "immutable", &params.buckets_immutable, "Make the hash buckets immutable"),
OPT_UINTEGER('t', "threads", &params.nthreads, "Specify amount of threads"),
OPT_UINTEGER('r', "runtime", &params.runtime, "Specify runtime (in seconds)"),
OPT_UINTEGER('f', "futexes", &params.nfutexes, "Specify amount of futexes per threads"),
@@ -118,6 +123,7 @@ static void print_summary(void)
printf("%sAveraged %ld operations/sec (+- %.2f%%), total secs = %d\n",
!params.silent ? "\n" : "", avg, rel_stddev_stats(stddev, avg),
(int)bench__runtime.tv_sec);
+ futex_print_nbuckets(&params);
}

int bench_futex_hash(int argc, const char **argv)
@@ -161,6 +167,7 @@ int bench_futex_hash(int argc, const char **argv)

if (!params.fshared)
futex_flag = FUTEX_PRIVATE_FLAG;
+ futex_set_nbuckets_param(&params);

printf("Run summary [PID %d]: %d threads, each operating on %d [%s] futexes for %d secs.\n\n",
getpid(), params.nthreads, params.nfutexes, params.fshared ? "shared":"private", params.runtime);
diff --git a/tools/perf/bench/futex-lock-pi.c b/tools/perf/bench/futex-lock-pi.c
index 0416120..5144a15 100644
--- a/tools/perf/bench/futex-lock-pi.c
+++ b/tools/perf/bench/futex-lock-pi.c
@@ -41,10 +41,13 @@ static struct stats throughput_stats;
static struct cond thread_parent, thread_worker;

static struct bench_futex_parameters params = {
+ .nbuckets = -1,
.runtime = 10,
};

static const struct option options[] = {
+ OPT_INTEGER( 'b', "buckets", &params.nbuckets, "Specify amount of hash buckets"),
+ OPT_BOOLEAN( 'I', "immutable", &params.buckets_immutable, "Make the hash buckets immutable"),
OPT_UINTEGER('t', "threads", &params.nthreads, "Specify amount of threads"),
OPT_UINTEGER('r', "runtime", &params.runtime, "Specify runtime (in seconds)"),
OPT_BOOLEAN( 'M', "multi", &params.multi, "Use multiple futexes"),
@@ -67,6 +70,7 @@ static void print_summary(void)
printf("%sAveraged %ld operations/sec (+- %.2f%%), total secs = %d\n",
!params.silent ? "\n" : "", avg, rel_stddev_stats(stddev, avg),
(int)bench__runtime.tv_sec);
+ futex_print_nbuckets(&params);
}

static void toggle_done(int sig __maybe_unused,
@@ -203,6 +207,7 @@ int bench_futex_lock_pi(int argc, const char **argv)
mutex_init(&thread_lock);
cond_init(&thread_parent);
cond_init(&thread_worker);
+ futex_set_nbuckets_param(&params);

threads_starting = params.nthreads;
gettimeofday(&bench__start, NULL);
diff --git a/tools/perf/bench/futex-requeue.c b/tools/perf/bench/futex-requeue.c
index aad5bfc..a2f91ee 100644
--- a/tools/perf/bench/futex-requeue.c
+++ b/tools/perf/bench/futex-requeue.c
@@ -42,6 +42,7 @@ static unsigned int threads_starting;
static int futex_flag = 0;

static struct bench_futex_parameters params = {
+ .nbuckets = -1,
/*
* How many tasks to requeue at a time.
* Default to 1 in order to make the kernel work more.
@@ -50,6 +51,8 @@ static struct bench_futex_parameters params = {
};

static const struct option options[] = {
+ OPT_INTEGER( 'b', "buckets", &params.nbuckets, "Specify amount of hash buckets"),
+ OPT_BOOLEAN( 'I', "immutable", &params.buckets_immutable, "Make the hash buckets immutable"),
OPT_UINTEGER('t', "threads", &params.nthreads, "Specify amount of threads"),
OPT_UINTEGER('q', "nrequeue", &params.nrequeue, "Specify amount of threads to requeue at once"),
OPT_BOOLEAN( 's', "silent", &params.silent, "Silent mode: do not display data/details"),
@@ -77,6 +80,7 @@ static void print_summary(void)
params.nthreads,
requeuetime_avg / USEC_PER_MSEC,
rel_stddev_stats(requeuetime_stddev, requeuetime_avg));
+ futex_print_nbuckets(&params);
}

static void *workerfn(void *arg __maybe_unused)
@@ -204,6 +208,8 @@ int bench_futex_requeue(int argc, const char **argv)
if (params.broadcast)
params.nrequeue = params.nthreads;

+ futex_set_nbuckets_param(&params);
+
printf("Run summary [PID %d]: Requeuing %d threads (from [%s] %p to %s%p), "
"%d at a time.\n\n", getpid(), params.nthreads,
params.fshared ? "shared":"private", &futex1,
diff --git a/tools/perf/bench/futex-wake-parallel.c b/tools/perf/bench/futex-wake-parallel.c
index 4352e31..ee66482 100644
--- a/tools/perf/bench/futex-wake-parallel.c
+++ b/tools/perf/bench/futex-wake-parallel.c
@@ -57,9 +57,13 @@ static struct stats waketime_stats, wakeup_stats;
static unsigned int threads_starting;
static int futex_flag = 0;

-static struct bench_futex_parameters params;
+static struct bench_futex_parameters params = {
+ .nbuckets = -1,
+};

static const struct option options[] = {
+ OPT_INTEGER( 'b', "buckets", &params.nbuckets, "Specify amount of hash buckets"),
+ OPT_BOOLEAN( 'I', "immutable", &params.buckets_immutable, "Make the hash buckets immutable"),
OPT_UINTEGER('t', "threads", &params.nthreads, "Specify amount of threads"),
OPT_UINTEGER('w', "nwakers", &params.nwakes, "Specify amount of waking threads"),
OPT_BOOLEAN( 's', "silent", &params.silent, "Silent mode: do not display data/details"),
@@ -218,6 +222,7 @@ static void print_summary(void)
params.nthreads,
waketime_avg / USEC_PER_MSEC,
rel_stddev_stats(waketime_stddev, waketime_avg));
+ futex_print_nbuckets(&params);
}


@@ -291,6 +296,8 @@ int bench_futex_wake_parallel(int argc, const char **argv)
if (!params.fshared)
futex_flag = FUTEX_PRIVATE_FLAG;

+ futex_set_nbuckets_param(&params);
+
printf("Run summary [PID %d]: blocking on %d threads (at [%s] "
"futex %p), %d threads waking up %d at a time.\n\n",
getpid(), params.nthreads, params.fshared ? "shared":"private",
diff --git a/tools/perf/bench/futex-wake.c b/tools/perf/bench/futex-wake.c
index 49b3c89..8d6107f 100644
--- a/tools/perf/bench/futex-wake.c
+++ b/tools/perf/bench/futex-wake.c
@@ -42,6 +42,7 @@ static unsigned int threads_starting;
static int futex_flag = 0;

static struct bench_futex_parameters params = {
+ .nbuckets = -1,
/*
* How many wakeups to do at a time.
* Default to 1 in order to make the kernel work more.
@@ -50,6 +51,8 @@ static struct bench_futex_parameters params = {
};

static const struct option options[] = {
+ OPT_INTEGER( 'b', "buckets", &params.nbuckets, "Specify amount of hash buckets"),
+ OPT_BOOLEAN( 'I', "immutable", &params.buckets_immutable, "Make the hash buckets immutable"),
OPT_UINTEGER('t', "threads", &params.nthreads, "Specify amount of threads"),
OPT_UINTEGER('w', "nwakes", &params.nwakes, "Specify amount of threads to wake at once"),
OPT_BOOLEAN( 's', "silent", &params.silent, "Silent mode: do not display data/details"),
@@ -93,6 +96,7 @@ static void print_summary(void)
params.nthreads,
waketime_avg / USEC_PER_MSEC,
rel_stddev_stats(waketime_stddev, waketime_avg));
+ futex_print_nbuckets(&params);
}

static void block_threads(pthread_t *w, struct perf_cpu_map *cpu)
diff --git a/tools/perf/bench/futex.c b/tools/perf/bench/futex.c
new file mode 100644
index 0000000..02ae6c5
--- /dev/null
+++ b/tools/perf/bench/futex.c
@@ -0,0 +1,65 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <err.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <linux/prctl.h>
+#include <sys/prctl.h>
+
+#include "futex.h"
+
+void futex_set_nbuckets_param(struct bench_futex_parameters *params)
+{
+ int ret;
+
+ if (params->nbuckets < 0)
+ return;
+
+ ret = prctl(PR_FUTEX_HASH, PR_FUTEX_HASH_SET_SLOTS, params->nbuckets, params->buckets_immutable);
+ if (ret) {
+ printf("Requesting %d hash buckets failed: %d/%m\n",
+ params->nbuckets, ret);
+ err(EXIT_FAILURE, "prctl(PR_FUTEX_HASH)");
+ }
+}
+
+void futex_print_nbuckets(struct bench_futex_parameters *params)
+{
+ char *futex_hash_mode;
+ int ret;
+
+ ret = prctl(PR_FUTEX_HASH, PR_FUTEX_HASH_GET_SLOTS);
+ if (params->nbuckets >= 0) {
+ if (ret != params->nbuckets) {
+ if (ret < 0) {
+ printf("Can't query number of buckets: %m\n");
+ err(EXIT_FAILURE, "prctl(PR_FUTEX_HASH)");
+ }
+ printf("Requested number of hash buckets does not currently used.\n");
+ printf("Requested: %d in usage: %d\n", params->nbuckets, ret);
+ err(EXIT_FAILURE, "prctl(PR_FUTEX_HASH)");
+ }
+ if (params->nbuckets == 0) {
+ ret = asprintf(&futex_hash_mode, "Futex hashing: global hash");
+ } else {
+ ret = prctl(PR_FUTEX_HASH, PR_FUTEX_HASH_GET_IMMUTABLE);
+ if (ret < 0) {
+ printf("Can't check if the hash is immutable: %m\n");
+ err(EXIT_FAILURE, "prctl(PR_FUTEX_HASH)");
+ }
+ ret = asprintf(&futex_hash_mode, "Futex hashing: %d hash buckets %s",
+ params->nbuckets,
+ ret == 1 ? "(immutable)" : "");
+ }
+ } else {
+ if (ret <= 0) {
+ ret = asprintf(&futex_hash_mode, "Futex hashing: global hash");
+ } else {
+ ret = asprintf(&futex_hash_mode, "Futex hashing: auto resized to %d buckets",
+ ret);
+ }
+ }
+ if (ret < 0)
+ err(EXIT_FAILURE, "ENOMEM, futex_hash_mode");
+ printf("%s\n", futex_hash_mode);
+ free(futex_hash_mode);
+}
diff --git a/tools/perf/bench/futex.h b/tools/perf/bench/futex.h
index ebdc2b0..9c9a73f 100644
--- a/tools/perf/bench/futex.h
+++ b/tools/perf/bench/futex.h
@@ -25,6 +25,8 @@ struct bench_futex_parameters {
unsigned int nfutexes;
unsigned int nwakes;
unsigned int nrequeue;
+ int nbuckets;
+ bool buckets_immutable;
};

/**
@@ -143,4 +145,7 @@ futex_cmp_requeue_pi(u_int32_t *uaddr, u_int32_t val, u_int32_t *uaddr2,
val, opflags);
}

+void futex_set_nbuckets_param(struct bench_futex_parameters *params);
+void futex_print_nbuckets(struct bench_futex_parameters *params);
+
#endif /* _FUTEX_H */