From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Frederic Weisbecker <fweisbec@gmail.com>
Cc: "Kirill A. Shutemov" <kirill@shutemov.name>,
linux-kernel@vger.kernel.org,
Dipankar Sarma <dipankar@in.ibm.com>,
Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@elte.hu>,
Peter Zijlstra <a.p.zijlstra@chello.nl>,
Lai Jiangshan <laijs@cn.fujitsu.com>
Subject: Re: linux-next-20110923: warning kernel/rcutree.c:1833
Date: Sun, 2 Oct 2011 17:28:32 -0700 [thread overview]
Message-ID: <20111003002832.GC2539@linux.vnet.ibm.com> (raw)
In-Reply-To: <20111002225019.GA1835@somewhere>
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
next prev parent reply other threads:[~2011-10-03 0:28 UTC|newest]
Thread overview: 57+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-09-25 0:24 linux-next-20110923: warning kernel/rcutree.c:1833 Kirill A. Shutemov
2011-09-25 5:08 ` Paul E. McKenney
2011-09-25 11:26 ` Kirill A. Shutemov
2011-09-25 13:06 ` Frederic Weisbecker
2011-09-25 14:19 ` Kirill A. Shutemov
2011-09-25 16:48 ` Paul E. McKenney
2011-09-26 1:04 ` Frederic Weisbecker
2011-09-26 1:10 ` Frederic Weisbecker
2011-09-26 1:26 ` Paul E. McKenney
2011-09-26 1:41 ` Paul E. McKenney
2011-09-26 9:39 ` Frederic Weisbecker
2011-09-26 22:34 ` Paul E. McKenney
2011-09-27 12:07 ` Frederic Weisbecker
2011-09-26 9:42 ` Frederic Weisbecker
2011-09-26 22:35 ` Paul E. McKenney
2011-09-26 9:20 ` Frederic Weisbecker
2011-09-26 22:50 ` Paul E. McKenney
2011-09-27 12:16 ` Frederic Weisbecker
2011-09-27 18:01 ` Paul E. McKenney
2011-09-28 12:31 ` Frederic Weisbecker
2011-09-28 18:40 ` Paul E. McKenney
2011-09-28 23:46 ` Frederic Weisbecker
2011-09-29 0:55 ` Paul E. McKenney
2011-09-29 4:49 ` Paul E. McKenney
2011-09-29 12:30 ` Frederic Weisbecker
2011-09-29 17:12 ` Paul E. McKenney
2011-09-29 17:19 ` Paul E. McKenney
2011-09-29 23:18 ` Paul E. McKenney
2011-09-30 13:11 ` Frederic Weisbecker
2011-09-30 15:29 ` Paul E. McKenney
2011-09-30 19:24 ` Paul E. McKenney
2011-10-01 4:34 ` Paul E. McKenney
2011-10-01 12:24 ` Frederic Weisbecker
2011-10-01 12:28 ` Frederic Weisbecker
2011-10-01 16:35 ` Paul E. McKenney
2011-10-01 17:07 ` Paul E. McKenney
2011-10-02 3:23 ` Paul E. McKenney
2011-10-02 11:45 ` Frederic Weisbecker
2011-10-02 22:50 ` Frederic Weisbecker
2011-10-03 0:28 ` Paul E. McKenney [this message]
2011-10-03 12:59 ` Frederic Weisbecker
2011-10-03 16:22 ` Paul E. McKenney
2011-10-03 17:11 ` Frederic Weisbecker
2011-10-02 23:07 ` Frederic Weisbecker
2011-10-03 0:32 ` Paul E. McKenney
2011-10-03 13:03 ` Frederic Weisbecker
2011-10-03 16:30 ` Paul E. McKenney
2011-10-06 0:58 ` Paul E. McKenney
2011-10-06 1:59 ` Paul E. McKenney
2011-10-06 12:11 ` Frederic Weisbecker
2011-10-06 18:44 ` Paul E. McKenney
2011-10-06 23:44 ` Paul E. McKenney
2011-09-26 1:25 ` Paul E. McKenney
2011-09-26 8:48 ` Frederic Weisbecker
2011-09-26 8:49 ` Frederic Weisbecker
2011-09-26 22:30 ` Paul E. McKenney
2011-09-27 11:55 ` Frederic Weisbecker
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