lkml.org 
[lkml]   [2013]   [Jun]   [5]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH v2] sched: fix clear NOHZ_BALANCE_KICK
On Wed, Jun 05, 2013 at 10:13:11AM +0200, Vincent Guittot wrote:
> I have faced a sequence where the Idle Load Balance was sometime not
> triggered for a while on my platform.
>
> CPU 0 and CPU 1 are running tasks and CPU 2 is idle
>
> CPU 1 kicks the Idle Load Balance
> CPU 1 selects CPU 2 as the new Idle Load Balancer
> CPU 2 sets NOHZ_BALANCE_KICK for CPU 2
> CPU 2 sends a reschedule IPI to CPU 2
> While CPU 3 wakes up, CPU 0 or CPU 1 migrates a waking up task A on CPU 2
> CPU 2 finally wakes up, runs task A and discards the Idle Load Balance
> task A quickly goes back to sleep (before a tick occurs on CPU 2)
> CPU 2 goes back to idle with NOHZ_BALANCE_KICK set
>
> Whenever CPU 2 will be selected as the ILB, no reschedule IPI will be sent
> because NOHZ_BALANCE_KICK is already set and no Idle Load Balance will be
> performed.
>
> We must wait for the sched softirq to be raised on CPU 2 thanks to another
> part the kernel to come back to clear NOHZ_BALANCE_KICK.
>
> The proposed solution clears NOHZ_BALANCE_KICK in schedule_ipi if
> we can't raise the sched_softirq for the Idle Load Balance.
>
> Change since V1:
> - move the clear of NOHZ_BALANCE_KICK in got_nohz_idle_kick if the ILB
> can't run on this CPU (as suggested by Peter)
>
> Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>

Thanks!


\
 
 \ /
  Last update: 2013-06-05 13:21    [W:0.032 / U:0.244 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site