linux-kernel - Re: [PATCHv7 01/11] clockevents: Prefer CPU local devices over global devices

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Date:	Wed, 19 Jun 2013 09:30:43 -0700
From:	Stephen Boyd <sboyd@...eaurora.org>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Mark Rutland <mark.rutland@....com>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-msm@...r.kernel.org" <linux-arm-msm@...r.kernel.org>,
	John Stultz <john.stultz@...aro.org>, arm@...nel.org,
	"soren.brinkmann@...inx.com" <soren.brinkmann@...inx.com>
Subject: Re: [PATCHv7 01/11] clockevents: Prefer CPU local devices over
 global devices

Thomas,

On 06/18, Mark Rutland wrote:
> On Thu, Jun 13, 2013 at 07:39:50PM +0100, Stephen Boyd wrote:
> > On 06/13, Thomas Gleixner wrote:
> > > On Thu, 13 Jun 2013, Daniel Lezcano wrote:
> > > > I prefer Thomas to have a look at it and ack it. I changed Cc to To for
> > > > Thomas.
> > > 
> > > The patch does not apply on tip timers/core. The code has been
> > > reworked a month ago. Please work against tip timers/core. That's
> > > where this stuff ends up.
> > > 
> > 
> > Ah, I thought your patch series had stalled. Here is a refreshed
> > patch. Every other patch in this series applies cleanly to tip
> > timers/core so I don't want to resend them again unless
> > absolutely necessary.
> > 
> > -----8<-----
> > Subject: [PATCH v8] clockevents: Prefer CPU local devices over global devices
> > 
> > On an SMP system with only one global clockevent and a dummy
> > clockevent per CPU we run into problems. We want the dummy
> > clockevents to be registered as the per CPU tick devices, but
> > we can only achieve that if we register the dummy clockevents
> > before the global clockevent or if we artificially inflate the
> > rating of the dummy clockevents to be higher than the rating
> > of the global clockevent. Failure to do so leads to boot
> > hangs when the dummy timers are registered on all other CPUs
> > besides the CPU that accepted the global clockevent as its tick
> > device and there is no broadcast timer to poke the dummy
> > devices.
> > 
> > If we're registering multiple clockevents and one clockevent is
> > global and the other is local to a particular CPU we should
> > choose to use the local clockevent regardless of the rating of
> > the device. This way, if the clockevent is a dummy it will take
> > the tick device duty as long as there isn't a higher rated tick
> > device and any global clockevent will be bumped out into
> > broadcast mode, fixing the problem described above.
> > 
> > Reported-by: Mark Rutland <mark.rutland@....com>
> > Cc: John Stultz <john.stultz@...aro.org>
> > Cc: Thomas Gleixner <tglx@...utronix.de>
> > Cc: Daniel Lezcano <daniel.lezcano@...aro.org>
> > Signed-off-by: Stephen Boyd <sboyd@...eaurora.org>
> 
> I've just tested this atop of tip/timers/core on a tc2, using only the
> sp804. As previously, without the patch boot hangs, and with the patch
> I'm able to reach userspace and do useful things.
> 
> Tested-by: Mark Rutland <mark.rutland@....com>
> 
> Thanks for working on this, Stephen.

Can you pick up the first two patches in this series please? And
preferably make a stable branch that can be pulled into arm-soc?
Then I can send the rest through the arm-soc tree.

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