From: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
To: Petr Mladek <pmladek@suse.com>
Cc: Viresh Kumar <viresh.kumar@linaro.org>,
Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
Andrew Morton <akpm@linux-foundation.org>,
Jan Kara <jack@suse.com>, Tejun Heo <tj@kernel.org>,
Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Byungchul Park <byungchul.park@lge.com>,
Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Subject: Re: [PATCH v12 0/3] printk: Make printk() completely async
Date: Wed, 13 Jul 2016 01:46:50 +0900 [thread overview]
Message-ID: <20160712164650.GA451@swordfish> (raw)
In-Reply-To: <20160712155918.GC8597@pathway.suse.cz>
On (07/12/16 17:59), Petr Mladek wrote:
[..]
> > [ 12.874909] sched: RT throttling activated for rt_rq ffffffc0ac13fcd0 (cpu 0)
> > [ 12.874909] potential CPU hogs:
> > [ 12.874909] printk (292)
> >
> > On my system, the excessive printing happens during suspend/resume and this
> > happened after all the non-boot CPUs were offlined. So, only CPU 0 was left and
> > that was doing printing for a long time and so these errors :)
> >
> > It resulted in missing some print messages eventually as the scheduler probably
> > didn't schedule this thread for sometime after that.
> >
> > Will it be fine to get the priority of this kthread to a somewhat lower value,
> > etc ?
>
> I think that this patch helped only by chance. It causes that any
> message without a new line will force printk to the sync mode.
> Then it will print even the buffered messages immediately. It
> causes printk to behave more or less in the sync mode all the time.
KERN_CONT messages are not so often, because they are not SMP-safe, any intruding
non-KERN_CONT message will wake_up() printk_kthread. there is a chance, you are
right, that printk will operate in sync mode for some time, when we would want it
to be async, so 0004 probably better try harder.
but KERN_CONT is not what's going on in this case, I think. at lest
"[ 12.874909] printk (292)" line suggests so -- printk was in async
mode... and somehow non-preemptible for some time... a delay from spin_lock()
in call_console_drivers()->write()?... but why would async printk worsen it.
> I am still scratching my head about the problem fixed by this patch
> and also about suspend problems.
yeah, quite puzzled myself. thanks Petr and Viresh for digging this up.
I need some sleep now, it's 2 am here, will return back tomorrow.
-ss
next prev parent reply other threads:[~2016-07-12 16:47 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-05-13 13:18 [PATCH v12 0/3] printk: Make printk() completely async Sergey Senozhatsky
2016-05-13 13:18 ` [PATCH v12 1/3] " Sergey Senozhatsky
2016-05-13 13:18 ` [PATCH v12 2/3] printk: Make wake_up_klogd_work_func() async Sergey Senozhatsky
2016-05-13 13:18 ` [PATCH v12 3/3] printk: make printk.synchronous param rw Sergey Senozhatsky
2016-06-09 2:20 ` [PATCH v12 0/3] printk: Make printk() completely async Sergey Senozhatsky
2016-06-29 5:08 ` Sergey Senozhatsky
2016-06-29 5:16 ` Joe Perches
2016-06-29 5:32 ` Sergey Senozhatsky
2016-07-12 16:28 ` Petr Mladek
2016-07-13 7:42 ` Sergey Senozhatsky
2016-07-13 11:14 ` Petr Mladek
2016-07-13 13:24 ` Sergey Senozhatsky
2016-07-13 14:22 ` Petr Mladek
2016-07-11 19:25 ` Viresh Kumar
2016-07-12 15:59 ` Petr Mladek
2016-07-12 16:46 ` Sergey Senozhatsky [this message]
2016-07-12 17:04 ` Viresh Kumar
2016-07-13 11:19 ` Petr Mladek
-- strict thread matches above, loose matches on Subject: below --
2016-04-22 13:52 Sergey Senozhatsky
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