linux-kernel - Re: Re: [RFC PATCH] suspend/resume performance improvement

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Date:	Wed, 27 May 2015 10:38:10 +0000 (GMT)
From:	EunTaik Lee <eun.taik.lee@...sung.com>
To:	Pavel Machek <pavel@....cz>
Cc:	"rjw@...ysocki.net" <rjw@...ysocki.net>,
	"len.brown@...el.com" <len.brown@...el.com>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: Re: [RFC PATCH] suspend/resume performance improvement


On Tue 2015-05-27 16:50 (GMT+09:00), Pavel Machek wrote:

>> So, instead of depending on a userspace task's time
>> slice, let kworker do the work to avoid a long wait
>> on the runqueue.
>
>...so if you really want high priority for that operation, just renice
>yourself to higher priority or something...

The problem occured on Android L version. KK had autosuspend enabled
but it was disabled in L to allow userspace to collect stats.

The delay was inside try_to_freeze_tasks function (at system_server thread of system_server process).
system_server got preempted after unlocking the tasklist_lock.
 46         while (true) {
 47                 todo = 0;
 48                 read_lock(&tasklist_lock);
 49                 for_each_process_thread(g, p) {
 50                         if (p == current || !freeze_task(p))
 51                                 continue;
 52 
 53                         if (!freezer_should_skip(p))
 54                                 todo++;
 55                 }
 56                 read_unlock(&tasklist_lock);

All of the threads of system_server process that was on the runqueue did not run during this period.
Freezing of tasks resumed after other tasks went out of the runqueue.

I have tested with the lowest nice value but the problem was still, although less, reproducible.

Best Regards,
Euntaik Lee