linux-kernel - Re: [PATCH 1/3] perf: add calls to suspend trace point

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Message-ID: <AANLkTim_ekCNw6xhC_MGY7=gfXUCfinXkLeXtttpHaGc@mail.gmail.com>
Date:	Tue, 4 Jan 2011 16:00:05 +0100
From:	Jean Pihet <jean.pihet@...oldbits.com>
To:	Pavel Machek <pavel@....cz>
Cc:	mingo@...e.hu, trenn@...e.de, Len Brown <len.brown@...el.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	linux-pm@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
	linux-omap@...r.kernel.org,
	Arjan van de Ven <arjan@...ux.intel.com>,
	linux-perf-users@...r.kernel.org, Jean Pihet <j-pihet@...com>
Subject: Re: [PATCH 1/3] perf: add calls to suspend trace point

Hi,

On Tue, Jan 4, 2011 at 12:29 PM, Pavel Machek <pavel@....cz> wrote:
> Hi!
>
>> Uses the machine_suspend trace point, called from the
>> generic kernel suspend_enter function.
>>
>> Signed-off-by: Jean Pihet <j-pihet@...com>
>> CC: Thomas Renninger <trenn@...e.de>
>> ---
>>  kernel/power/suspend.c |    3 +++
>>  1 files changed, 3 insertions(+), 0 deletions(-)
>>
>> diff --git a/kernel/power/suspend.c b/kernel/power/suspend.c
>> index ecf7705..0650596 100644
>> --- a/kernel/power/suspend.c
>> +++ b/kernel/power/suspend.c
>> @@ -22,6 +22,7 @@
>>  #include <linux/mm.h>
>>  #include <linux/slab.h>
>>  #include <linux/suspend.h>
>> +#include <trace/events/power.h>
>>
>>  #include "power.h"
>>
>> @@ -164,7 +165,9 @@ static int suspend_enter(suspend_state_t state)
>>       error = sysdev_suspend(PMSG_SUSPEND);
>>       if (!error) {
>>               if (!suspend_test(TEST_CORE) && pm_check_wakeup_events()) {
>> +                     trace_machine_suspend(state);
>>                       error = suspend_ops->enter(state);
>> +                     trace_machine_suspend(PWR_EVENT_EXIT);
>>                       events_check_enabled = false;
>>               }
>>               sysdev_resume();
>
> Ok... why this place?
This trace has been placed here because it traces the machine low
level mode enter.

> I mean, perhaps suspend time should include
> device suspend?
That makes sense. We have a few options here:
1) keep the traces as proposed to trace the low level machine code only,
2) move the traces to the entry and exit of suspend_enter so that it
includes the prepare and late_prepare (+ the associated wake-up)
callbacks as well,
3) move the traces to suspend_devices_and_enter so that it includes 2)
and the handling of the console and the devices,
4) move the traces to enter_state do that it includes 3), the call to
sys_sync and the user space freeze.

Note that the the SNAPSHOT_2RAM ioctl code also calls
suspend_devices_and_enter, so if only 4) is used no trace will be
generated in that case.

I am in favor of 3) of 4).
What do you think?

>                                                                        Pavel
> --
> (english) http://www.livejournal.com/~pavelmachek
> (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
>

Thanks,
Jean
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