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Date: Mon, 9 Jun 2008 02:35:18 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: "Jakub W. Jozwicki" <jozwicki@...er.pl>
Cc: linux-kernel@...r.kernel.org
Subject: Re: sched_yield() on 2.6.25
On Sun, 8 Jun 2008 13:34:10 +0200 "Jakub W. Jozwicki" <jozwicki@...er.pl> wrote:
> Hello,
> I observe strange behavior of sched_yield() on 2.6.25 (strange comparing to
> 2.6.24). Here is the code (available at
> http://systest.googlecode.com/files/systest20080119.tgz):
>
> ------------------------------------------------------
> timer_t timer;
> sig_atomic_t cnt = 0;
> long long sum = 0;
> long times[21], min, max;
> pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
> struct timespec ts = { 0, 0 };
> pthread_t last_th = 0;
>
> void *th_proc(void* p) {
> int n = SIZE(times) -1;
> pthread_t th;
>
> while(1) {
> pthread_mutex_lock(&mutex);
> th = pthread_self();
> if (pthread_equal(th,last_th)) {
> pthread_mutex_unlock(&mutex);
> sched_yield();
> continue;
> }
> rt_timer_stop(&ts);
> last_th = th;
> if (cnt>=1) {
> times[cnt-1] = ts_sum(&ts);
> if (cnt <= n) {
> sum += times[cnt-1];
> box(times[cnt-1],min,max);
> #define uint unsigned int
> printf("[%u] Thread switching time: %ldns\n",(uint)th, times[cnt-1]);
> }
> else {
> printf("[%u] Thread switching time (not counted): %ldns\n",(uint)th,
> times[cnt-1]);
> }
> cnt--;
> }
> ....
> -----------------------------------------------------
> and here are the results:
>
> Setting cpu mask to 1
>
> -- SYSTEM INFO -------------------
>
> localhost: Linux 2.6.24-rt4 #8 SMP PREEMPT RT Mon Jan 21 18:45:00 CET 2008
>
> Setting priority SCHED_OTHER to 0 (normal process) for 20802
> [3084102544] Thread switching time (not counted): 10709015ns
> [3075709840] Thread switching time: 35468301ns
> [3084102544] Thread switching time: 2793ns
> [3075709840] Thread switching time 30725ns
> [3084102544] Thread switching time: 10405ns
> [3075709840] Thread switching time: 2724ns
> [3084102544] Thread switching time: 2654ns
> [3075709840] Thread switching time: 2653ns
> [3084102544] Thread switching time: 3352ns
> [3075709840] Thread switching time: 2583ns
> [3084102544] Thread switching time: 2514ns
> [3075709840] Thread switching time: 2514ns
It would save us some time if you were to tell us what these results
mean, please.
--
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