Minki/linux
1
0
Fork 1
mirror of https://github.com/torvalds/linux.git synced 2024-11-11 14:42:24 +00:00
Code Issues Packages Projects Releases Wiki Activity

sched: Fix idle_cpu()

Browse Source 
On -rt we observed hackbench waking all 400 tasks to a single cpu.
This is because of select_idle_sibling()'s interaction with the new
ipi based wakeup scheme.

The existing idle_cpu() test only checks to see if the current task on
that cpu is the idle task, it does not take already queued tasks into
account, nor does it take queued to be woken tasks into account.

If the remote wakeup IPIs come hard enough, there won't be time to
schedule away from the idle task, and would thus keep thinking the cpu
was in fact idle, regardless of the fact that there were already
several hundred tasks runnable.

We couldn't reproduce on mainline, but there's no reason it couldn't
happen.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/n/tip-3o30p18b2paswpc9ohy2gltp@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Thomas Gleixner 2011-09-15 15:32:06 +02:00 committed by Ingo Molnar
parent f0f1d32f93
commit 908a328372
1 changed files with 14 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

15
kernel/sched.c
View File

@ -5138,7 +5138,20 @@ EXPORT_SYMBOL(task_nice);
*/
int idle_cpu(int cpu)
{
return cpu_curr(cpu) == cpu_rq(cpu)->idle;
struct rq *rq = cpu_rq(cpu);
if (rq->curr != rq->idle)
return 0;
if (rq->nr_running)
return 0;
#ifdef CONFIG_SMP
if (!llist_empty(&rq->wake_list))
return 0;
#endif
return 1;
}
/**