linux-kernel - Re: [PATCH 0/4] time: dynamic irq affinity

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Date:	Sun, 10 Mar 2013 23:03:56 +0530
From:	Santosh Shilimkar <santosh.shilimkar@...com>
To:	Daniel Lezcano <daniel.lezcano@...aro.org>
CC:	<john.stultz@...aro.org>, <tglx@...utronix.de>,
	<viresh.kumar@...aro.org>, <jacob.jun.pan@...ux.intel.com>,
	<linux-arm-kernel@...ts.infradead.org>, <linux-pm@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <linaro-kernel@...ts.linaro.org>,
	<patches@...aro.org>, <linus.walleij@...ricsson.com>
Subject: Re: [PATCH 0/4] time: dynamic irq affinity

On Wednesday 27 February 2013 03:47 AM, Daniel Lezcano wrote:
> When a cpu goes to a deep idle state where its local timer is shutdown,
> it notifies the time framework to use the broadcast timer instead.
> 
> Unfortunately, the broadcast device could wake up any CPU, including an
> idle one which is not concerned by the wake up at all.
> 
> This implies, in the worst case, an idle CPU will wake up to send an IPI
> to another idle cpu.
> 
> This patch solves this by setting the irq affinity to the cpu concerned
> by the nearest timer event, by this way, the CPU which is wake up is
> guarantee to be the one concerned by the next event and we are safe with
> unnecessary wakeup for another idle CPU.
> 
> As the irq affinity is not supported by all the archs, a flag is needed
> to specify which clocksource can handle it.
> 
> Daniel Lezcano (3):
>   time : pass broadcast parameter
>   time : set broadcast irq affinity
>   ARM: nomadik: add dynamic irq flag to the timer
> 
> Viresh Kumar (1):
>   ARM: timer-sp: Set dynamic irq affinity
> 
Thanks Daniel for addressing the comments from earlier version. This
version looks good to me.

Reviewed-by: Santosh Shilimkar <santosh.shilimkar@...com>

Regards,
Santosh
P.S: As I mentioned 'CLOCK_EVT_FEAT_DYNIRQ' optimization on
OMAP at least I found risky because you might end up missing
the asynchronous IPI wakeups because of the current SGI's
implementation. This must be true for other ARM platforms
as well.

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