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Subject[PATCH] selftests/seccomp: Pin benchmark to single CPU
Date
The seccomp benchmark test (for validating the benefit of bitmaps) can
be sensitive to scheduling speed, so pin the process to a single CPU,
which appears to significantly improve reliability.

Reported-by: kernel test robot <oliver.sang@intel.com>
Closes: https://lore.kernel.org/oe-lkp/202402061002.3a8722fd-oliver.sang@intel.com
Cc: Mark Brown <broonie@kernel.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Will Drewry <wad@chromium.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
---
.../selftests/seccomp/seccomp_benchmark.c | 27 +++++++++++++++++++
1 file changed, 27 insertions(+)

diff --git a/tools/testing/selftests/seccomp/seccomp_benchmark.c b/tools/testing/selftests/seccomp/seccomp_benchmark.c
index 5b5c9d558dee..d0b733e708cc 100644
--- a/tools/testing/selftests/seccomp/seccomp_benchmark.c
+++ b/tools/testing/selftests/seccomp/seccomp_benchmark.c
@@ -4,7 +4,9 @@
*/
#define _GNU_SOURCE
#include <assert.h>
+#include <err.h>
#include <limits.h>
+#include <sched.h>
#include <stdbool.h>
#include <stddef.h>
#include <stdio.h>
@@ -119,6 +121,29 @@ long compare(const char *name_one, const char *name_eval, const char *name_two,
return good ? 0 : 1;
}

+/* Pin to a single CPU so the benchmark won't bounce around the system. */
+void affinity(void)
+{
+ long cpu;
+ ulong ncores = sysconf(_SC_NPROCESSORS_CONF);
+ cpu_set_t *setp = CPU_ALLOC(ncores);
+ ulong setsz = CPU_ALLOC_SIZE(ncores);
+
+ /* Set from highest CPU down. */
+ for (cpu = ncores - 1; cpu >= 0; cpu--) {
+ CPU_ZERO_S(setsz, setp);
+ CPU_SET_S(cpu, setsz, setp);
+ if (sched_setaffinity(getpid(), setsz, setp) == -1)
+ continue;
+ printf("Pinned to CPU %lu of %lu\n", cpu + 1, ncores);
+ goto out;
+ }
+ fprintf(stderr, "Could not set CPU affinity -- calibration may not work well");
+
+out:
+ CPU_FREE(setp);
+}
+
int main(int argc, char *argv[])
{
struct sock_filter bitmap_filter[] = {
@@ -153,6 +178,8 @@ int main(int argc, char *argv[])
system("grep -H . /proc/sys/net/core/bpf_jit_enable");
system("grep -H . /proc/sys/net/core/bpf_jit_harden");

+ affinity();
+
if (argc > 1)
samples = strtoull(argv[1], NULL, 0);
else
--
2.34.1

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