Re: [PATCH][GIT PULL] tracing: Fix compile issue for trace_sched_wakeup.c

Jason Baron
2010-10-22T14:14:34Z

On Fri, Oct 22, 2010 at 10:14:31AM +0200, Peter Zijlstra wrote:
> On Thu, 2010-10-21 at 21:44 -0400, Jason Baron wrote:
>
> > I finally found that we actually continue to run after the above
> > apparent 'hang'. That is, we continue to make progress updating the jump
> > labels. And doing a dump of all the system tasks at the time of the hang
> > showed the processes in various places besides the stop machine threads.
> > Thus, I thought that perhaps, for some reason the stop machine threads
> > weren't being scheduled.
> >
> > Thus, I tried commenting out the special scheduling that is set up for
> > stop machine threads, and that fixed the hang. I haven't yet looked into
> > what might be going wrong with that scheduling...but maybe somebody else
> > knows...
>
> Hrmm, so are you saying rq->stop was runnable but not running?

yes, that's what it seems like.

>
> That would imply broken wakeup-preemption, does something like the below
> cure that?
>
>

no still seeing the same hang with the below patch...also, as a data point I
backed out the patch that adds the stop_sched_class and that resolved the hang
as well - just as a data point.

thanks,

-Jason

> ---
> kernel/sched_stoptask.c | 1 +
> 1 files changed, 1 insertions(+), 0 deletions(-)
>
> diff --git a/kernel/sched_stoptask.c b/kernel/sched_stoptask.c
> index 45bddc0..50ad10f 100644
> --- a/kernel/sched_stoptask.c
> +++ b/kernel/sched_stoptask.c
> @@ -35,6 +35,7 @@ static struct task_struct *pick_next_task_stop(struct rq *rq)
> static void
> enqueue_task_stop(struct rq *rq, struct task_struct *p, int flags)
> {
> + resched_cpu(cpu_of(rq));
> }
>
> static void
>
>