linux-kernel - Re: [PATCH] cpuidle: Consolidate disabled state checks

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Message-ID: <20191104115201.GG4131@hirez.programming.kicks-ass.net>
Date:   Mon, 4 Nov 2019 12:52:01 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     "Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:     Linux PM <linux-pm@...r.kernel.org>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Doug Smythies <dsmythies@...us.net>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] cpuidle: Consolidate disabled state checks

On Mon, Nov 04, 2019 at 12:16:17PM +0100, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> 
> There are two reasons why CPU idle states may be disabled: either
> because the driver has disabled them or because they have been
> disabled by user space via sysfs.
> 
> In the former case, the state's "disabled" flag is set once during
> the initialization of the driver and it is never cleared later (it
> is read-only effectively).  In the latter case, the "disable" field
> of the given state's cpuidle_state_usage struct is set and it may be
> changed via sysfs.  Thus checking whether or not an idle state has
> been disabled involves reading these two flags every time.
> 
> In order to avoid the additional check of the state's "disabled" flag
> (which is effectively read-only anyway), use the value of it at the
> init time to set a (new) flag in the "disable" field of that state's
> cpuidle_state_usage structure and use the sysfs interface to
> manipulate another (new) flag in it.  This way the state is disabled
> whenever the "disable" field of its cpuidle_state_usage structure is
> nonzero, whatever the reason, and it is the only place to look into
> to check whether or not the state has been disabled.
> 
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> Acked-by: Daniel Lezcano <daniel.lezcano@...aro.org>

Much thanks, that always bugged me.

Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>