linux-kernel - Re: [PATCH] cpuidle: Do not use CPUIDLE_DRIVER_STATE

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Date:	Wed, 27 May 2015 10:22:17 +0200
From:	Daniel Lezcano <daniel.lezcano@...aro.org>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Linux PM list <linux-pm@...r.kernel.org>
CC:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Len Brown <len.brown@...el.com>,
	Preeti U Murthy <preeti@...ux.vnet.ibm.com>
Subject: Re: [PATCH] cpuidle: Do not use CPUIDLE_DRIVER_STATE_START in cpuidle.c

On 05/27/2015 03:36 AM, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
>
> The CPUIDLE_DRIVER_STATE_START symbol is defined as 1 only if
> CONFIG_ARCH_HAS_CPU_RELAX is set, otherwise it is defined as 0.
> However, if CONFIG_ARCH_HAS_CPU_RELAX is set, the first (index 0)
> entry in the cpuidle driver's table of states is overwritten with
> the default "poll" entry by the core.  The "state" defined by the
> "poll" entry doesn't provide ->enter_dead and ->enter_freeze
> callbacks and its exit_latency is 0.
>
> For this reason, it is not necessary to use CPUIDLE_DRIVER_STATE_START
> in cpuidle_play_dead() (->enter_dead is NULL, so the "poll state"
> will be skipped by the loop) and in find_deepest_state() (since
> exit_latency is 0, the "poll state" will become the default if the
> "s->exit_latency <= latency_req" check is replaced with
> "s->exit_latency < latency_req" which may only matter for drivers
> providing different states with the same exit_latency).
>
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>

I was about to send *exactly* the same patch :)

Acked-by: Daniel Lezcano <daniel.lezcano@...aro.org>


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