From mboxrd@z Thu Jan 1 00:00:00 1970 From: santosh.shilimkar@ti.com (Santosh Shilimkar) Date: Mon, 25 Feb 2013 11:42:48 +0530 Subject: too many timer retries happen when do local timer swtich with broadcast timer In-Reply-To: References: <51263975.20906@ti.com> <5127436E.4040100@ti.com> <20130222103149.GC12140@e102568-lin.cambridge.arm.com> <51275058.7010809@ti.com> <20130222144829.GG12140@e102568-lin.cambridge.arm.com> <20130222152639.GH12140@e102568-lin.cambridge.arm.com> Message-ID: <512B00E0.8030801@ti.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Saturday 23 February 2013 12:22 AM, Thomas Gleixner wrote: > 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. >>>> I too confirm that the warnings cause is same. >>>> 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. > I agree that 2 is better alternative to avoid multiple changes. Whichever alternative you choose, will be happy to test it :) Regards, Santosh