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

[Sameer Nanda]

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.  I am thinking of adding time_delta to
all three traces.  That way we should get the space saving while still
allowing quick spotting of devices that take long time to resume.

>
>> [1]: here's an example script I use for sorting the device resume times:
>> cat /sys/kernel/debug/tracing/trace | grep device_resume_out | awk
>> 'BEGIN { FS = "time_delta=" } ; { print $2 $0 }' | sort -n
>>
>
> Question is, how often is this done? And that 5k is permanent for all
> users.
>
> -- Steve
>
>



-- 
Sameer
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