linux-kernel - Re: [PATCH V3] cpuidle: Handle tick_broadcast

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Message-ID: <554CAF7A.6060609@arm.com>
Date:	Fri, 08 May 2015 13:43:38 +0100
From:	Sudeep Holla <sudeep.holla@....com>
To:	Preeti U Murthy <preeti@...ux.vnet.ibm.com>
CC:	"peterz@...radead.org" <peterz@...radead.org>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"rafael.j.wysocki@...el.com" <rafael.j.wysocki@...el.com>,
	"daniel.lezcano@...aro.org" <daniel.lezcano@...aro.org>,
	Sudeep Holla <sudeep.holla@....com>,
	"rlippert@...gle.com" <rlippert@...gle.com>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"linus.walleij@...aro.org" <linus.walleij@...aro.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [PATCH V3] cpuidle: Handle tick_broadcast_enter() failure gracefully



On 08/05/15 08:35, Preeti U Murthy wrote:
> When a CPU has to enter an idle state where tick stops, it makes a call
> to tick_broadcast_enter(). The call will fail if this CPU is the
> broadcast CPU. Today, under such a circumstance, the arch cpuidle code
> handles this CPU.  This is not convincing because not only do we not
> know what the arch cpuidle code does, but we also do not account for the
> idle state residency time and usage of such a CPU.
>
> This scenario can be handled better by simply choosing an idle state
> where in ticks do not stop. To accommodate this change move the setting
> of runqueue idle state from the core to the cpuidle driver, else the
> rq->idle_state will be set wrong.
>
> Signed-off-by: Preeti U Murthy <preeti@...ux.vnet.ibm.com>

I gave it a spin on ARM64 Juno platform with one of the CPU in broadcast
mode and Vexpress TC2 with broadcast timer. I found no issues in both
the cases. So, you can add:

Tested-by: Sudeep Holla <sudeep.holla@....com>

Regards,
Sudeep
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