Messages in this thread |  | | | Date | Sun, 2 Oct 2011 17:28:32 -0700 | | From | "Paul E. McKenney" <> | | Subject | Re: linux-next-20110923: warning kernel/rcutree.c:1833 |
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On Mon, Oct 03, 2011 at 12:50:22AM +0200, Frederic Weisbecker wrote: > On Fri, Sep 30, 2011 at 12:24:38PM -0700, Paul E. McKenney wrote: > > @@ -328,11 +326,11 @@ static int rcu_implicit_offline_qs(struct rcu_data *rdp) > > return 1; > > } > > > > - /* If preemptible RCU, no point in sending reschedule IPI. */ > > - if (rdp->preemptible) > > - return 0; > > - > > - /* The CPU is online, so send it a reschedule IPI. */ > > + /* > > + * The CPU is online, so send it a reschedule IPI. This forces > > + * it through the scheduler, and (inefficiently) also handles cases > > + * where idle loops fail to inform RCU about the CPU being idle. > > + */ > > If the idle loop forgets to call rcu_idle_enter() before going to > sleep, I don't know if it's a good idea to try to cure that situation > by forcing a quiescent state remotely. It may make the thing worse > because we actually won't notice the lack of call to rcu_idle_enter() > that the rcu stall detector would otherwise report to us. > > Also I don't think that works. If the task doesn't have > TIF_RESCHED, it won't go through the scheduler on irq exit. > smp_send_reschedule() doesn't set the flag. And also scheduler_ipi() > returns right away if no wake up is pending. > > So, other than resuming the idle loop to sleep again, nothing may happen. > > Or am I missing something?
Hmmm... Seems like the IPIs aren't helping in any case, then?
I suppose that I could do an smp_call_function_single(), which then did a set_need_resched()...
But this is a separate issue that I need to deal with. That said, any suggestions are welcome!
Thanx, Paul
> > if (rdp->cpu != smp_processor_id()) > > smp_send_reschedule(rdp->cpu); > > else
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