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

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Date:	Wed, 5 Jan 2011 00:01:23 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Jean Pihet <jean.pihet@...oldbits.com>
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 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?

Rafael
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