linux-kernel - Re: [PATCH 0/3] Add generic idle notifiers

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Date:	Thu, 07 Jul 2011 15:34:38 -0700
From:	Kevin Hilman <khilman@...com>
To:	Todd Poynor <toddpoynor@...gle.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Russell King <linux@....linux.org.uk>,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	Colin Cross <ccross@...roid.com>
Subject: Re: [PATCH 0/3] Add generic idle notifiers

Todd Poynor <toddpoynor@...gle.com> writes:

> On Thu, Jul 07, 2011 at 10:05:10AM -0700, Kevin Hilman wrote:
>> Todd Poynor <toddpoynor@...gle.com> writes:
>> 
>> > Add notifiers for idle entry and exit, called with IDLE_START when a
>> > CPU goes idle and IDLE_END when it goes out of idle, based on the
>> > existing idle notifiers for the x86_64 arch.
>> >
>> > Convert x86_64 to use these notifiers, and call the notifiers on ARM.
>> >
>> > Convert the ARM LEDs events for idle start/end to these notifiers.
>> 
>> Is this intended to replace the more general CPU PM notifiers proposed
>> by Colin:
>> 
>> http://lists.infradead.org/pipermail/linux-arm-kernel/2011-June/052827.html
>
> This is intended to coexist with the CPU PM notifiers.  The idle
> notifiers proposed here are notifying of a change in kernel scheduler
> state: the scheduler has no task to run and is entering its "idle
> loop", or now has something to run and is exiting idle state.
> Things that can use this include power management hints such as the
> existing drivers/idle/i7300_idle.c usage, the ARM LEDs idle triggers,
> and there's probably other existing potential uses in other arch'es that
> I should go track down.
>
> The CPU PM notifiers notify of changes in hardware power state that
> affect the CPU and closely associated IP blocks (such as an OMAP
> power state transition that causes one or more CPU power domains to
> hit OFF).  These changes may be due to cpuidle power state management
> when the system is idle, or may be due to suspending or resuming the
> system (such as a suspend-to-RAM), or may be due to a CPU hotplug event.
> In the case of an idle loop entry, if cpuidle decides it is not
> appropriate to change CPU power state (as when insufficient time
> remains until next timer expiry to enter such a power state due to
> entry and exit latency), there may be no CPU PM notification
> generated.  The callbacks for CPU PM notifiers on ARM do things such
> as save/restore GIC interrupt controller state and VFP floating-point
> coprocessor state.
>
> That's the intent, anyhow, but ideas are welcome, thanks,

OK, thanks for the clarification.

Kevin
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