linux-kernel - Re: [PATCH] tracing, perf: add more power related events

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Message-ID: <AANLkTik08ezo2ui-P7mSqSt4VR6wzWYH0hAyNTZALbi0@mail.gmail.com>
Date:	Tue, 7 Sep 2010 09:28:56 +0200
From:	Jean Pihet <jean.pihet@...oldbits.com>
To:	Thomas Renninger <trenn@...e.de>
Cc:	discuss@...swatts.org, linux-pm@...ts.linux-foundation.org,
	Ingo Molnar <mingo@...e.hu>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Len Brown <len.brown@...el.com>, arjan@...radead.org,
	Kevin Hilman <khilman@...prootsystems.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tracing, perf: add more power related events

Hi Thomas,

On Mon, Sep 6, 2010 at 2:00 PM, Thomas Renninger <trenn@...e.de> wrote:
> On Monday 06 September 2010 13:27:13 Jean Pihet wrote:
>> On Mon, Sep 6, 2010 at 12:42 PM, Thomas Renninger <trenn@...e.de> wrote:
> ...
>> In order to reach an efficient low power mode you
>> need to ensure that all clocks in a clock domain are idled or cut off
>> (automatically by the HW or with the intervention of SW drivers).
>>
>> The HW complexity requires the tracing of all those clocks/power
>> states, that is why new events are proposed.
> Hm, but if the HW can switch clocks behind your back, how do you
> realize that to throw a perf clock power event then?
Such clocks are automatically shut off when there is no activity on
the module, this allows the system to reach a lower power state. All
that is needed is to ensure the modules are correctly configured to
shut off unneeded clocks automatically.

> Theoretically you need to poll to keep track of HW switching the
> clocks?
No. I would not poll hundreds of clocks.
Furthermore there is no event to be thrown away, in the case the
reached power mode is not 'deep' enough you need a trace point showing
what blocked the transition. There is still work to do to achieve
that, it is coming soon.

>
>    Thomas
>

Note: a re-spin of the patch has been sent on a new thread.

Jean
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