linux-kernel - Re: [PATCH 2/3] perf: add OMAP support for the new power events

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Date:	Wed, 5 Jan 2011 11:56:08 +0100
From:	Jean Pihet <jean.pihet@...oldbits.com>
To:	Nishanth Menon <nm@...com>
Cc:	mingo@...e.hu, linux-kernel@...r.kernel.org, trenn@...e.de,
	linux-omap@...r.kernel.org,
	Arjan van de Ven <arjan@...ux.intel.com>,
	linux-perf-users@...r.kernel.org, rjw@...k.pl,
	Jean Pihet <j-pihet@...com>
Subject: Re: [PATCH 2/3] perf: add OMAP support for the new power events

On Tue, Jan 4, 2011 at 7:03 PM, Nishanth Menon <nm@...com> wrote:
> jean.pihet@...oldbits.com had written, on 01/04/2011 04:17 AM, the
> following:
> [..]
>>
>> diff --git a/arch/arm/mach-omap2/pm34xx.c b/arch/arm/mach-omap2/pm34xx.c
>> index 0ec8a04..0ee0b0e 100644
>> --- a/arch/arm/mach-omap2/pm34xx.c
>> +++ b/arch/arm/mach-omap2/pm34xx.c
>> @@ -29,6 +29,7 @@
>>  #include <linux/delay.h>
>>  #include <linux/slab.h>
>>  #include <linux/console.h>
>> +#include <trace/events/power.h>
>>  #include <plat/sram.h>
>>  #include <plat/clockdomain.h>
>> @@ -506,8 +507,14 @@ static void omap3_pm_idle(void)
>>        if (omap_irq_pending() || need_resched())
>>                goto out;
>>  +      trace_power_start(POWER_CSTATE, 1, smp_processor_id());
>> +       trace_cpu_idle(1, smp_processor_id());
>> +
>>        omap_sram_idle();
>>  +      trace_power_end(smp_processor_id());
>> +       trace_cpu_idle(PWR_EVENT_EXIT, smp_processor_id());
>
> Dumb question: it just tells me which C state was attempted - not if
> actually succeeded in hitting it rt? Does'nt this give us a false data?
Yes this tracks the idle requests only. The actual hit state might be
different depending on various factors: HW state, enabled clocks,
power domains dependencies etc.
Debugging the actual PM hit state requires other tools, which could
use the trace API. There is definitely more to come on that topic.

>
> [..]
>>
>> diff --git a/arch/arm/plat-omap/clock.c b/arch/arm/plat-omap/clock.c
>> index fc62fb5..7cbb09b 100644
>> --- a/arch/arm/plat-omap/clock.c
>> +++ b/arch/arm/plat-omap/clock.c
>
> (from an offline discussion on a related topic): Would it also be nice to
> hook on mach-omap2/clock.c points as well to hook on indirect changes?
> [..]
>
> --
> Regards,
> Nishanth Menon
>
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