[v2] Add random locking benchmark
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Patch applied to master at the time it was sent
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| dj/TryBot-32bit |
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Build for i686
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Commit Message
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.
---
Comments
On 8/22/22 11:14, Wilco Dijkstra via Libc-alpha wrote:
> 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.
Suggest:
... This relies on the implementation of random
using internal locks to access shared global data, and that the runtime
enables locking once a single thread has been created.
~~~
I think this needs a few more explanatory comments. A lot of other people
look at our benchmarks and might scratch their heads at this one.
Post a v3 and I'll ACK that.
>
> ---
>
> 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 \
OK.
> # 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.
OK.
> + 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"
> +
We could run the benchmark for a fixed amount of time, rather than a
fixed number of iterations, see bench-skeleton.c and DURATION.
Suggest:
/* Arbitrarily pick 20M such that we can measure the time taken. */
> +#define NUM_ITERS 20000000
OK.
> +
> +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);
OK. Seed to 0.
Suggest:
/* Warmup. Arbitrarily pick 1/4 of iterations. */
> + 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);
OK.
> +
> + 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;
Suggest:
/* We assume the runtimes decision to keep the library multi-threaded
once a single thread has launched, and not change back to
single-threaded. */
Provides a little more context to this section, even though
you mention 'SINGLE_THREAD_P == false' later.
> + pthread_create (&t, NULL, thread_start, NULL);
> + pthread_join (t, NULL);
OK. We are now in multi-threaded and will never switch back to the
single threaded case.
> +
> + /* 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"
> +
>
>
>
>
Hi Carlos,
> We could run the benchmark for a fixed amount of time, rather than a
> fixed number of iterations, see bench-skeleton.c and DURATION.
Unfortunately bench-skeleton is way too difficult to use - I'd just want to
give it a few functions to benchmark and let it do the rest. So it needs
cleaning up before benchmarks can use it without a magic python script.
I've updated the comments, see v3 below.
Cheers,
Wilco
v3: Improve comments
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, and that the runtime
uses multi-threaded locking once a thread has been created (even after
it finishes).
---
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..c0aecb7f95b9f185df3bba7a75e3ef0884dbf6ce
--- /dev/null
+++ b/benchtests/bench-random-lock.c
@@ -0,0 +1,109 @@
+/* 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"
+
+/* Modern cores run 20M iterations in about 1 second. */
+#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);
+
+ /* Warmup to reduce variations due to frequency scaling. */
+ 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");
+
+ /* Start a short thread to force SINGLE_THREAD_P == false. This relies on
+ the runtime disabling single-threaded optimizations when multiple
+ threads are used, even after they finish. */
+
+ pthread_t t;
+ pthread_create (&t, NULL, thread_start, NULL);
+ pthread_join (t, NULL);
+
+ /* Repeat benchmark with single-threaded optimizations disabled. */
+ 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"
+
ping
From: Wilco Dijkstra <Wilco.Dijkstra@arm.com>
Sent: 24 August 2022 15:43
To: Carlos O'Donell <carlos@redhat.com>; 'GNU C Library' <libc-alpha@sourceware.org>
Subject: Re: [PATCH v2] Add random locking benchmark
Hi Carlos,
> We could run the benchmark for a fixed amount of time, rather than a
> fixed number of iterations, see bench-skeleton.c and DURATION.
Unfortunately bench-skeleton is way too difficult to use - I'd just want to
give it a few functions to benchmark and let it do the rest. So it needs
cleaning up before benchmarks can use it without a magic python script.
I've updated the comments, see v3 below.
Cheers,
Wilco
v3: Improve comments
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, and that the runtime
uses multi-threaded locking once a thread has been created (even after
it finishes).
---
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..c0aecb7f95b9f185df3bba7a75e3ef0884dbf6ce
--- /dev/null
+++ b/benchtests/bench-random-lock.c
@@ -0,0 +1,109 @@
+/* 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"
+
+/* Modern cores run 20M iterations in about 1 second. */
+#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);
+
+ /* Warmup to reduce variations due to frequency scaling. */
+ 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");
+
+ /* Start a short thread to force SINGLE_THREAD_P == false. This relies on
+ the runtime disabling single-threaded optimizations when multiple
+ threads are used, even after they finish. */
+
+ pthread_t t;
+ pthread_create (&t, NULL, thread_start, NULL);
+ pthread_join (t, NULL);
+
+ /* Repeat benchmark with single-threaded optimizations disabled. */
+ 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"
+
On Fri, Dec 9, 2022 at 5:59 AM Wilco Dijkstra via Libc-alpha
<libc-alpha@sourceware.org> wrote:
>
>
> ping
>
> From: Wilco Dijkstra <Wilco.Dijkstra@arm.com>
> Sent: 24 August 2022 15:43
> To: Carlos O'Donell <carlos@redhat.com>; 'GNU C Library' <libc-alpha@sourceware.org>
> Subject: Re: [PATCH v2] Add random locking benchmark
>
> Hi Carlos,
>
> > We could run the benchmark for a fixed amount of time, rather than a
> > fixed number of iterations, see bench-skeleton.c and DURATION.
>
> Unfortunately bench-skeleton is way too difficult to use - I'd just want to
> give it a few functions to benchmark and let it do the rest. So it needs
> cleaning up before benchmarks can use it without a magic python script.
>
> I've updated the comments, see v3 below.
>
> Cheers,
> Wilco
>
> v3: Improve comments
>
> 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, and that the runtime
> uses multi-threaded locking once a thread has been created (even after
> it finishes).
>
> ---
> 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..c0aecb7f95b9f185df3bba7a75e3ef0884dbf6ce
> --- /dev/null
> +++ b/benchtests/bench-random-lock.c
> @@ -0,0 +1,109 @@
> +/* 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"
> +
> +/* Modern cores run 20M iterations in about 1 second. */
> +#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);
> +
> + /* Warmup to reduce variations due to frequency scaling. */
> + 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");
> +
> + /* Start a short thread to force SINGLE_THREAD_P == false. This relies on
> + the runtime disabling single-threaded optimizations when multiple
> + threads are used, even after they finish. */
Is it worth benchmarking with some contention or is the goal
just SINGLE_THREAD_P true/false?
> +
> + pthread_t t;
> + pthread_create (&t, NULL, thread_start, NULL);
> + pthread_join (t, NULL);
> +
> + /* Repeat benchmark with single-threaded optimizations disabled. */
> + 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"
> +
Can you remove this extra line.
```
Applying: Add random locking benchmark
.git/rebase-apply/patch:120: new blank line at EOF.
+
warning: 1 line adds whitespace errors.
```
Hi Noah,
> + /* Start a short thread to force SINGLE_THREAD_P == false. This relies on
> + the runtime disabling single-threaded optimizations when multiple
> + threads are used, even after they finish. */
> Is it worth benchmarking with some contention or is the goal
> just SINGLE_THREAD_P true/false?
The latter, the goal is just to test singlethreaded is faster and multithreaded
is not slower. We could add a benchmark for the internal locks (which might
test contention cases), but trying to use the internal headers in benchtests
seems non-trivial.
> +
> Can you remove this extra line.
I don't remember ever seeing that, another oddity of git apply...
I'll remove it in the next version.
Cheers,
Wilco
On Fri, Dec 9, 2022 at 10:15 AM Wilco Dijkstra <Wilco.Dijkstra@arm.com> wrote:
>
> Hi Noah,
>
> > + /* Start a short thread to force SINGLE_THREAD_P == false. This relies on
> > + the runtime disabling single-threaded optimizations when multiple
> > + threads are used, even after they finish. */
>
> > Is it worth benchmarking with some contention or is the goal
> > just SINGLE_THREAD_P true/false?
>
> The latter, the goal is just to test singlethreaded is faster and multithreaded
> is not slower. We could add a benchmark for the internal locks (which might
> test contention cases), but trying to use the internal headers in benchtests
> seems non-trivial.
>
Fair enough (reviewed this patch w.o seeing your next one initially so
was missing the context).
> > +
> > Can you remove this extra line.
>
> I don't remember ever seeing that, another oddity of git apply...
> I'll remove it in the next version.
>
> Cheers,
> Wilco
@@ -236,6 +236,7 @@ hash-benchset := \
stdlib-benchset := \
arc4random \
strtod \
+ random-lock \
# stdlib-benchset
stdio-common-benchset := sprintf
new file mode 100644
@@ -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"
+