linux-kernel - Re: [RFC PATCH] power: Add option to log time spent in suspend

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Date:	Thu, 2 May 2013 12:11:50 -0700
From:	Colin Cross <ccross@...roid.com>
To:	John Stultz <john.stultz@...aro.org>
Cc:	Pavel Machek <pavel@....cz>,
	Zoran Markovic <zoran.markovic@...aro.org>,
	lkml <linux-kernel@...r.kernel.org>,
	Linux PM list <linux-pm@...r.kernel.org>,
	Android Kernel Team <kernel-team@...roid.com>,
	Todd Poynor <toddpoynor@...gle.com>,
	San Mehat <san@...gle.com>, Benoit Goby <benoit@...roid.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>, Len Brown <len.brown@...el.com>
Subject: Re: [RFC PATCH] power: Add option to log time spent in suspend

On Thu, May 2, 2013 at 11:58 AM, John Stultz <john.stultz@...aro.org> wrote:
> On 05/02/2013 11:29 AM, Colin Cross wrote:
>>
>> On Thu, May 2, 2013 at 5:27 AM, Pavel Machek <pavel@....cz> wrote:
>>>
>>>
>>>> dmesg is not the solution, it's not a stable api, it would require
>>>> constant parsing to make sure you didn't miss data before it fell out
>>>> of the ringbuffer, and sched_clock often does not (and should not)
>>>> tick during suspend, so printk times don't show the time spent
>>>> suspended.
>>>
>>> If timing info printed is invalid, that should be fixed.
>>
>> It's not invalid, its just not measuring the time that is useful here.
>>   printk is measuring something similar to (but not exactly the same
>> as) CLOCK_MONOTONIC, but this is measuring something similar to
>> CLOCK_BOOTTIME.
>
>
> One thing I'm curious about with this patch, since we measure and keep track
> of suspend time in the timekeeping core, there may be enough justification
> to adding this sort of debugging info the timekeeping core itself.
>
> Although what is being tracked with this driver isn't just total time in
> suspend, but looks like more of a logarithmic histogram of suspend times. Is
> there any context you can provide as to why that particular format was
> chosen (which would could be added to help improve the commit message)?

The idea was to keep a minimal amount of data while still being able
to see how often the device is waking up.
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