Re: [PATCH] power, trace: add tracing for device_resume

[Sameer Nanda]

On Sat, May 19, 2012 at 12:30 PM, Rafael J. Wysocki <rjw@xxxxxxx> wrote:
> On Saturday, May 19, 2012, Greg KH wrote:
>> On Sat, May 19, 2012 at 01:59:20PM +0200, Rafael J. Wysocki wrote:
>> > On Saturday, May 19, 2012, Sameer Nanda wrote:
>> > > On Fri, May 18, 2012 at 4:01 PM, Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> wrote:
>> > > > On Fri, May 18, 2012 at 03:17:32PM -0700, Sameer Nanda wrote:
>> > > >> On Fri, May 18, 2012 at 2:46 PM, Rafael J. Wysocki <rjw@xxxxxxx> wrote:
>> > > >> > On Friday, May 18, 2012, Sameer Nanda wrote:
>> > > >> >> On Fri, May 18, 2012 at 2:19 PM, Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:
>> > > >> >> > On Fri, 2012-05-18 at 13:58 -0700, Sameer Nanda wrote:
>> > > >> >> >> On Fri, May 18, 2012 at 12:14 PM, Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:
>> > > >> >> >> > On Fri, 2012-05-18 at 11:57 -0700, Sameer Nanda wrote:
>> > > >> >> >> >
>> > > >> >> >> >> AFAICT, they are used for something completely different -- help solve
>> > > >> >> >> >> suspend/resume issues by saving a hash in the RTC of the last device
>> > > >> >> >> >> that suspended/resumed. ÂThey don't use the perf tracing mechanism at
>> > > >> >> >> >> all.
>> > > >> >> >> >>
>> > > >> >> >> >
>> > > >> >> >> > Also note that all tracepoints have timestamps attached to them. You do
>> > > >> >> >> > not need to add deltas. Do that in the userspace tools that read the
>> > > >> >> >> > timestamps and events. This way you can have one DECLARE_EVENT_CLASS and
>> > > >> >> >> > three DEFINE_EVENTs. This will save space.
>> > > >> >> >>
>> > > >> >> >> Agreed on the space savings. ÂHowever, with the time_delta in the
>> > > >> >> >> trace message itself, a one line shell script [1] that sorts on the
>> > > >> >> >> time_delta field is sufficient to quickly spot the devices that take a
>> > > >> >> >> long time to resume. ÂWithout the time_delta field, the user tool is
>> > > >> >> >> more complex since it needs to first match up the device_resume_in,
>> > > >> >> >> device_resume_waited and device_resume_out traces and then calculate
>> > > >> >> >> time deltas.
>> > > >> >> >>
>> > > >> >> >> Seems like a worthwhile trade-off to me but I can take out the
>> > > >> >> >> time_delta if the general consensus is otherwise.
>> > > >> >> >
>> > > >> >> > Just note that every TRACE_EVENT() adds around 5k or more code. Every
>> > > >> >> > DEFINE_EVENT adds just about 300 bytes.
>> > > >> >>
>> > > >> >> Ok, let me respin the patch. ÂI am thinking of adding time_delta to
>> > > >> >> all three traces. ÂThat way we should get the space saving while still
>> > > >> >> allowing quick spotting of devices that take long time to resume.
>> > > >> >
>> > > >> > Well, what's wrong with the code in drivers/base/power/main.c that
>> > > >> > is activated by adding initcall_debug to the kernel command line?
>> > > >>
>> > > >> Mostly that I hadn't looked closely at initcall_debug before writing my patch :)
>> > > >>
>> > > >> Now that I have taken a look at it, the main issue is that the kernel
>> > > >> command line needs to be modified to activate it. ÂWe cannot do this
>> > > >> for our automated regression suites since the kernel command line is
>> > > >> protected on Chrome OS systems.
>> > > >
>> > > > You are kidding, right? ÂYou have control over your test systems, don't
>> > > > bloat everyone's kernel by 5k just because your infrastructure is
>> > > > somehow something that you feel you can't change.
>> > >
>> > > Fair enough. ÂBut having to modify the kernel command line to do this
>> > > is clunky. ÂHow about exposing the ability to turn on these
>> > > initcall_debug prints through a knob under /sys/power?
>> >
>> > This might work, but first you'd need to make them depend on something
>> > different from initcall_debug (and make that thing in turn be set if
>> > initcall_debug is put into the kernel command line). ÂThen, you could
>> > export the new variable.
>> >
>> > Greg, does that make sense to you?
>>
>> Maybe, I'd like to see a patch first before agreeing with it though :)
>
> Sure.

New patch uploaded that uses the existing initcall_debug functionality.


-- 
Sameer
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/