Re: too many timer retries happen when do local timer swtich withbroadcast timer

[Santosh Shilimkar]

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
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/