From: tglx@linutronix.de (Thomas Gleixner)
To: linux-arm-kernel@lists.infradead.org
Subject: too many timer retries happen when do local timer swtich with broadcast timer
Date: Fri, 22 Feb 2013 19:52:14 +0100 (CET) [thread overview]
Message-ID: <alpine.LFD.2.02.1302221946070.22263@ionos> (raw)
In-Reply-To: <20130222152639.GH12140@e102568-lin.cambridge.arm.com>
On Fri, 22 Feb 2013, Lorenzo Pieralisi wrote:
> On Fri, Feb 22, 2013 at 03:03:02PM +0000, Thomas Gleixner wrote:
> > On Fri, 22 Feb 2013, Lorenzo Pieralisi wrote:
> > > On Fri, Feb 22, 2013 at 12:07:30PM +0000, Thomas Gleixner wrote:
> > > > Now we could make use of that and avoid going deep idle just to come
> > > > back right away via the IPI. Unfortunately the notification thingy has
> > > > no return value, but we can fix that.
> > > >
> > > > To confirm that theory, could you please try the hack below and add
> > > > some instrumentation (trace_printk)?
> > >
> > > Applied, and it looks like that's exactly why the warning triggers, at least
> > > on the platform I am testing on which is a dual-cluster ARM testchip.
> > >
> > > There is a still time window though where the CPU (the IPI target) can get
> > > back to idle (tick_broadcast_pending still not set) before the CPU target of
> > > the broadcast has a chance to run tick_handle_oneshot_broadcast (and set
> > > tick_broadcast_pending), or am I missing something ?
> >
> > Well, the tick_broadcast_pending bit is uninteresting if the
> > force_broadcast bit is set. Because if that bit is set we know for
> > sure, that we got woken with the cpu which gets the broadcast timer
> > and raced back to idle before the broadcast handler managed to
> > send the IPI.
>
> Gah, my bad sorry, I mixed things up. I thought
>
> tick_check_broadcast_pending()
>
> was checking against the tick_broadcast_pending mask not
>
> tick_force_broadcast_mask
Yep, that's a misnomer. I just wanted to make sure that my theory is
correct. I need to think about the real solution some more.
We have two alternatives:
1) Make the clockevents_notify function have a return value.
2) Add something like the hack I gave you with a proper name.
The latter has the beauty, that we just need to modify the platform
independent idle code instead of going down to every callsite of the
clockevents_notify thing.
Thanks,
tglx
next prev parent reply other threads:[~2013-02-22 18:52 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-02-20 11:16 too many timer retries happen when do local timer swtich with broadcast timer Jason Liu
2013-02-20 13:33 ` Thomas Gleixner
2013-02-21 6:16 ` Jason Liu
2013-02-21 9:36 ` Thomas Gleixner
2013-02-21 10:50 ` Jason Liu
2013-02-21 13:48 ` Thomas Gleixner
2013-02-21 15:12 ` Santosh Shilimkar
2013-02-21 22:19 ` Thomas Gleixner
2013-02-22 10:07 ` Santosh Shilimkar
2013-02-22 10:24 ` Thomas Gleixner
2013-02-22 10:30 ` Santosh Shilimkar
2013-02-22 10:31 ` Lorenzo Pieralisi
2013-02-22 11:02 ` Santosh Shilimkar
2013-02-22 12:07 ` Thomas Gleixner
2013-02-22 14:48 ` Lorenzo Pieralisi
2013-02-22 15:03 ` Thomas Gleixner
2013-02-22 15:26 ` Lorenzo Pieralisi
2013-02-22 18:52 ` Thomas Gleixner [this message]
2013-02-25 6:12 ` Santosh Shilimkar
2013-02-25 6:38 ` Jason Liu
2013-02-25 13:34 ` Lorenzo Pieralisi
2013-02-22 10:28 ` Lorenzo Pieralisi
2013-02-22 10:26 ` Jason Liu
2013-02-21 10:35 ` Lorenzo Pieralisi
2013-02-21 10:49 ` Jason Liu
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