[PATCH v2] stdlib: Tuned down tst-arc4random-thread internal parameters

[PATCH v2] stdlib: Tuned down tst-arc4random-thread internal parameters

[Adhemerval Zanella]

With new arc4random implementation, the internal parameters might
require a lot of runtime and/or trigger some contention on older
kernels (which might trigger spurious timeout failures).

Also, since we are now testing getrandom entropy instead of an
userspace RNG, there is no much need to extensive testing.

With this change the tst-arc4random-thread goes from about 1m to
5s on a Ryzen 9 with 5.15.0-41-generic.

Checked on x86_64-linux-gnu.
---
 stdlib/tst-arc4random-thread.c | 19 ++++++++++++++-----
 1 file changed, 14 insertions(+), 5 deletions(-)

diff --git a/stdlib/tst-arc4random-thread.c b/stdlib/tst-arc4random-thread.c
index 3373d4d446..2441a44bf8 100644
--- a/stdlib/tst-arc4random-thread.c
+++ b/stdlib/tst-arc4random-thread.c
@@ -24,16 +24,16 @@
 #include <support/namespace.h>
 #include <support/support.h>
 #include <support/xthread.h>
+#include <unistd.h>
 
 /* Number of arc4random_buf calls per thread.  */
-enum { count_per_thread = 5000 };
+enum { count_per_thread = 2048 };
 
 /* Number of threads computing randomness.  */
-enum { inner_threads = 5 };
+enum { inner_threads = 4 };
 
-/* Number of threads launching other threads.  Chosen as to not to
-   overload the system.  */
-enum { outer_threads = 7 };
+/* Number of threads launching other threads.  */
+static int outer_threads = 1;
 
 /* Number of launching rounds performed by the outer threads.  */
 enum { outer_rounds = 10 };
@@ -331,6 +331,15 @@ do_test_func (const char *fname, void (*func)(unsigned char *, size_t))
 static int
 do_test (void)
 {
+  /* Do not run more threads than the maximum of online CPUs.  */
+  long int cpus = sysconf (_SC_NPROCESSORS_ONLN);
+  if (cpus != -1)
+    /* Limit the number to not overload the system.  */
+    outer_threads = (cpus / 2) / inner_threads ?: 1;
+
+  printf ("info: outer_threads=%d inner_threads=%d\n", outer_threads,
+	  inner_threads);
+
   do_test_func ("arc4random", generate_arc4random);
   do_test_func ("arc4random_buf", generate_arc4random_buf);
   do_test_func ("arc4random_uniform", generate_arc4random_uniform);
-- 
2.34.1

Re: [PATCH v2] stdlib: Tuned down tst-arc4random-thread internal parameters

[Szabolcs Nagy]

The 07/27/2022 10:10, Adhemerval Zanella via Libc-alpha wrote:
> +  /* Do not run more threads than the maximum of online CPUs.  */
> +  long int cpus = sysconf (_SC_NPROCESSORS_ONLN);
> +  if (cpus != -1)
> +    /* Limit the number to not overload the system.  */
> +    outer_threads = (cpus / 2) / inner_threads ?: 1;

on my glibc test system

$ getconf _NPROCESSORS_ONLN
160
$ nproc
16
$ taskset -c 0 getconf _NPROCESSORS_ONLN
160
$ taskset -c 0 nproc
1

this is in a cgroup with a fixed cpuset 0-15.

sched_getaffinity might be better for this.