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

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Message-ID: <20130502122747.GA22618@amd.pavel.ucw.cz>
Date:	Thu, 2 May 2013 14:27:47 +0200
From:	Pavel Machek <pavel@....cz>
To:	Colin Cross <ccross@...roid.com>
Cc:	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>,
	John Stultz <john.stultz@...aro.org>,
	"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

Hi!

> >> +#include <linux/debugfs.h>
> >> +#include <linux/err.h>
> >> +#include <linux/init.h>
> >> +#include <linux/kernel.h>
> >> +#include <linux/seq_file.h>
> >> +#include <linux/syscore_ops.h>
> >> +#include <linux/time.h>
> >> +
> >> +static struct timespec suspend_time_before;
> >> +static unsigned int time_in_suspend_bins[32];
> >> +
> >> +#ifdef CONFIG_DEBUG_FS
> >> +static int suspend_time_debug_show(struct seq_file *s, void *data)
> >> +{
> >> +     unsigned int bin;
> >> +     seq_printf(s, "      time (secs)        count\n");
> >> +     seq_printf(s, "------------------------------\n");
> >> +     for (bin = 0; bin < 32; bin++) {
> >> +             if (time_in_suspend_bins[bin] == 0)
> >> +                     continue;
> >> +             seq_printf(s, "%10u - %-10u %4u\n",
> >> +                     bin ? 1 << (bin - 1) : 0, 1 << bin,
> >> +                             time_in_suspend_bins[bin]);
> >> +     }
> >> +     return 0;
> >> +}
> >> +
> >> +static int suspend_time_debug_open(struct inode *inode, struct file *file)
> >> +{
> >> +     return single_open(file, suspend_time_debug_show, NULL);
> >> +}
> >
> > Ok, whole new driver to get timing info... As we already have times in
> > printk, can't existing printks() get the same info? Maybe
> > Documentation/ file describing how to get that info from dmesg would
> > be enough?
> 
> If this were to be merged I assume it would be rewritten directly into
> kernel/power/suspend.c instead of using syscore ops.  That was just
> done to ease future merges while it was out of tree.
> 
> 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.

									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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