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MINOR: debug: add a trivial PRNG for scheduler stress-tests

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Commit a5a447984 ("MINOR: debug: add "debug dev sched" to stress the
scheduler.") doesn't scale with threads because ha_random64() takes care
of being totally thread-safe for use with UUIDs. We don't need this for
the stress-testing functions, let's just implement a xorshift PRNG
instead. On 8 threads the performance jumped from 230k ctx/s with 96%
spent in ha_random64() to 14M ctx/s.
This commit is contained in:
Willy Tarreau 2020-11-30 16:17:33 +01:00
parent a5a4479849
commit 8a069eb9a4
1 changed files with 13 additions and 2 deletions
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15
src/debug.c
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@ -42,6 +42,17 @@
volatile unsigned long threads_to_dump = 0;
unsigned int debug_commands_issued = 0;
/* Xorshift RNGs from http://www.jstatsoft.org/v08/i14/paper */
static THREAD_LOCAL unsigned int y = 2463534242;
static unsigned int debug_prng()
{
y ^= y << 13;
y ^= y >> 17;
y ^= y << 5;
return y;
}
/* Dumps to the buffer some known information for the desired thread, and
* optionally extra info for the current thread. The dump will be appended to
* the buffer, so the caller is responsible for preliminary initializing it.
@ -684,7 +695,7 @@ static struct task *debug_task_handler(struct task *t, void *ctx, unsigned short
t->expire = tick_add(now_ms, inter);
/* half of the calls will wake up another entry */
rnd = ha_random64();
rnd = debug_prng();
if (rnd & 1) {
rnd >>= 1;
rnd %= tctx[0];
@ -706,7 +717,7 @@ static struct task *debug_tasklet_handler(struct task *t, void *ctx, unsigned sh
/* wake up two random entries */
for (i = 0; i < 2; i++) {
rnd = ha_random64() % tctx[0];
rnd = debug_prng() % tctx[0];
rnd = tctx[rnd + 2];
if (rnd & 1)