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@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20250416162921.513656-20-bigeasy@linutronix.de

1 files changed, 8 insertions, 1 deletions

diff --git a/tools/perf/bench/futex-wake-parallel.c b/tools/perf/bench/futex-wake-parallel.c
index 4352e318631e..ee66482c29fd 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",