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

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Date:	Tue, 30 Apr 2013 20:29:17 -0700
From:	Colin Cross <ccross@...roid.com>
To:	Pavel Machek <pavel@....cz>
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

On Tue, Apr 30, 2013 at 5:29 PM, Pavel Machek <pavel@....cz> wrote:
> Hi!
>
>> From: Colin Cross <ccross@...roid.com>
>>
>> Below is a patch from android kernel that maintains a histogram of
>> suspend times. Please review and provide feedback.
>>
>> Prints the time spent in suspend in the kernel log, and keeps statistics
>> on the time spent in suspend in /sys/kernel/debug/suspend_time
>>
>> Cc: Android Kernel Team <kernel-team@...roid.com>
>> Cc: Colin Cross <ccross@...roid.com>
>> Cc: Todd Poynor <toddpoynor@...gle.com>
>> Cc: San Mehat <san@...gle.com>
>> Cc: Benoit Goby <benoit@...roid.com>
>> Cc: John Stultz <john.stultz@...aro.org>
>> Cc: Pavel Machek <pavel@....cz>
>> Cc: Rafael J. Wysocki <rjw@...k.pl>
>> Cc: Len Brown <len.brown@...el.com>
>> Signed-off-by: Colin Cross <ccross@...roid.com>
>> Signed-off-by: Todd Poynor <toddpoynor@...gle.com>
>> [zoran.markovic@...aro.org: Re-formatted suspend time table to better fit
>> expected values, tweaked commit message]
>> Signed-off-by: Zoran Markovic <zoran.markovic@...aro.org>
>
>> +++ b/kernel/power/suspend_time.c
>> @@ -0,0 +1,111 @@
>> +/*
>> + * debugfs file to track time spent in suspend
>> + *
>> + * Copyright (c) 2011, Google, Inc.
>> + *
>> + * This program is free software; you can redistribute it and/or modify
>> + * it under the terms of the GNU General Public License as published by
>> + * the Free Software Foundation; either version 2 of the License, or
>> + * (at your option) any later version.
>> + *
>> + * This program is distributed in the hope that it will be useful, but WITHOUT
>> + * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
>> + * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
>> + * more details.
>> + */
>> +
>> +#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.
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