Messages in this thread Patch in this message | | | From | Anton Blanchard <> | Date | Sun, 11 Mar 2001 17:50:22 +1100 | Subject | Re: kernel lock contention and scalability |
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Hi,
> In the slow path of a spinlock_acquire they busy wait for a few > cycles, and then call schedule with a zero timeout assuming that > it'll basically do the same as a sched_yield() but more portably.
The obvious problem with this is that we bounce in and out of schedule() a few times before moving on to the next task. I see this also with sched_yield().
I had this patch lying around which I think came about when I was playing with pthreads (which for spinlocks does sched_yield() for a while before sleeping)
--- linux/kernel/sched.c Fri Mar 9 10:26:56 2001 +++ linux_intel/kernel/sched.c Fri Mar 9 08:42:39 2001 @@ -505,6 +505,9 @@ goto out_unlock; } #else + if (prev->policy & SCHED_YIELD) + prev->counter = (prev->counter >> 4); + prev->policy &= ~SCHED_YIELD; #endif /* CONFIG_SMP */ } Anton
/* test sched_yield */ #include <stdio.h> #include <sched.h> #include <sys/time.h> #include <sys/types.h> #include <unistd.h>
#undef USE_SELECT
void waste_time() { int i; for(i = 0; i < 10000; i++) ; } void do_stuff(int i) { #ifdef USE_SELECT struct timeval tv; #endif while(1) { fprintf(stderr, "%d\n", i); waste_time(); #ifdef USE_SELECT tv.tv_sec = 0; tv.tv_usec = 0; select(0, NULL, NULL, NULL, &tv); #else sched_yield(); #endif } } int main() { int i, pid; for(i = 0; i < 10; i++) { pid = fork(); if (!pid) do_stuff(i); } do_stuff(i+1);
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