[PATCH v2] Add random locking benchmark
Wilco Dijkstra
Wilco.Dijkstra@arm.com
Mon Aug 22 15:14:32 GMT 2022
v2: rename as suggested, use random throughout
Add a simple benchmark to measure the overhead of internal libc
locks in the random() implementation on both single- and
multi-threaded cases. This relies on the implementation of random
using internal locks to access shared global data.
---
diff --git a/benchtests/Makefile b/benchtests/Makefile
index d99771be74b40f8afa3953f61c0721b19658d4b7..c413eac1d23568cb88bf22c6e50303e24ec10ea0 100644
--- a/benchtests/Makefile
+++ b/benchtests/Makefile
@@ -236,6 +236,7 @@ hash-benchset := \
stdlib-benchset := \
arc4random \
strtod \
+ random-lock \
# stdlib-benchset
stdio-common-benchset := sprintf
diff --git a/benchtests/bench-random-lock.c b/benchtests/bench-random-lock.c
new file mode 100644
index 0000000000000000000000000000000000000000..13c8e77cbd3538bb1a15f81def0a2c41a3763729
--- /dev/null
+++ b/benchtests/bench-random-lock.c
@@ -0,0 +1,102 @@
+/* Benchmark internal libc locking functions used in random.
+ Copyright (C) 2022 Free Software Foundation, Inc.
+ This file is part of the GNU C Library.
+
+ The GNU C Library is free software; you can redistribute it and/or
+ modify it under the terms of the GNU Lesser General Public
+ License as published by the Free Software Foundation; either
+ version 2.1 of the License, or (at your option) any later version.
+
+ The GNU C Library is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public
+ License along with the GNU C Library; if not, see
+ <https://www.gnu.org/licenses/>. */
+
+#define TEST_MAIN
+#define TEST_NAME "random-lock"
+
+#include <pthread.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include "bench-timing.h"
+#include "json-lib.h"
+
+#define NUM_ITERS 20000000
+
+json_ctx_t json_ctx;
+
+
+/* Measure the overhead of __libc_lock_lock and __libc_lock_unlock by
+ calling random (). */
+static void
+bench_random_lock (size_t iters)
+{
+ timing_t start, stop, total;
+
+ srandom (0);
+ for (int i = 0; i < iters / 4; i++)
+ (void) random ();
+
+ TIMING_NOW (start);
+
+ for (int i = 0; i < iters; i++)
+ (void) random ();
+
+ TIMING_NOW (stop);
+
+ TIMING_DIFF (total, start, stop);
+
+ json_element_double (&json_ctx, (double) total / (double) iters);
+}
+
+static void *
+thread_start (void *p)
+{
+ return p;
+}
+
+int
+do_bench (void)
+{
+ json_init (&json_ctx, 0, stdout);
+
+ json_document_begin (&json_ctx);
+
+ json_attr_string (&json_ctx, "timing_type", TIMING_TYPE);
+ json_attr_object_begin (&json_ctx, "functions");
+ json_attr_object_begin (&json_ctx, "random");
+ json_attr_string (&json_ctx, "bench-variant", "single-threaded");
+ json_array_begin (&json_ctx, "results");
+
+ /* Run benchmark single threaded. */
+ bench_random_lock (NUM_ITERS);
+
+ json_array_end (&json_ctx);
+ json_attr_object_end (&json_ctx);
+
+ json_attr_object_begin (&json_ctx, "random");
+ json_attr_string (&json_ctx, "bench-variant", "multi-threaded");
+ json_array_begin (&json_ctx, "results");
+
+ pthread_t t;
+ pthread_create (&t, NULL, thread_start, NULL);
+ pthread_join (t, NULL);
+
+ /* Repeat benchmark now SINGLE_THREAD_P == false. */
+ bench_random_lock (NUM_ITERS);
+
+ json_array_end (&json_ctx);
+ json_attr_object_end (&json_ctx);
+ json_attr_object_end (&json_ctx);
+ json_document_end (&json_ctx);
+ return 0;
+}
+
+#define TEST_FUNCTION do_bench ()
+
+#include "../test-skeleton.c"
+
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