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

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Date:	Thu, 13 Jun 2013 13:16:35 -0700
From:	Sören Brinkmann <soren.brinkmann@...inx.com>
To:	Stephen Boyd <sboyd@...eaurora.org>
CC:	Thomas Gleixner <tglx@...utronix.de>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	<linux-arm-kernel@...ts.infradead.org>,
	<linux-kernel@...r.kernel.org>, <linux-arm-msm@...r.kernel.org>,
	John Stultz <john.stultz@...aro.org>,
	Mark Rutland <mark.rutland@....com>
Subject: Re: [PATCHv7 01/11] clockevents: Prefer CPU local devices over
 global devices

On Thu, Jun 13, 2013 at 11:39:50AM -0700, 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>
Tested-by: Sören Brinkmann <soren.brinkmann@...inx.com>

I retested my case on tip/timers/core with the same results.

	Sören


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