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

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Date:	Wed, 5 Jan 2011 11:09:35 +0100
From:	Jean Pihet <jean.pihet@...oldbits.com>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	Pavel Machek <pavel@....cz>, mingo@...e.hu, trenn@...e.de,
	Len Brown <len.brown@...el.com>,
	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

On Wed, Jan 5, 2011 at 12:01 AM, Rafael J. Wysocki <rjw@...k.pl> wrote:
> On Tuesday, January 04, 2011, Jean Pihet wrote:
>> 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?
>
> Why don't we keep the tracepoints as proposed _and_ add two additional
> tracepoints around device suspend-resume?
I like the idea but that requires to extend the current API with
additional suspend tracepoints or device state change tracepoints.
That can be done once the current API is firmly in place.
Today the only trace API for suspend is machine_suspend(unsigned int
state), so I think the best option is 3) here above.

Unless there is an objection I am pushing 3) asap.

Thanks!
Jean

>
> Rafael
> --
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