From: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
To: Petr Mladek <pmladek@suse.com>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>,
sergey.senozhatsky@gmail.com, jack@suse.com, tj@kernel.org,
kyle@kernel.org, davej@codemonkey.org.uk, calvinowens@fb.com,
akpm@linux-foundation.org, linux-mm@kvack.org, mhocko@kernel.org
Subject: Re: How to avoid printk() delay caused by cond_resched() ?
Date: Wed, 2 Mar 2016 23:34:15 +0900 [thread overview]
Message-ID: <20160302143415.GB614@swordfish> (raw)
In-Reply-To: <20160302133810.GB22171@pathway.suse.cz>
On (03/02/16 14:38), Petr Mladek wrote:
[..]
> >
> > CONFIG_PREEMPT_NONE=y
> > # CONFIG_PREEMPT_VOLUNTARY is not set
> > # CONFIG_PREEMPT is not set
> > CONFIG_PREEMPT_COUNT=y
>
> preempt_disable() / preempt_enable() would do the job.
> The question is where to put it. If you are concerned about
> the delay, you might want to disable preemption around
> the whole locked area, so that it works reasonable also
> in the preemptive kernel.
another question is why cond_resched() is suddenly so expensive?
my guess is because of OOM, so we switch to tasks that potentially
do direct reclaims, etc. if so, then even offloaded printk will take
a significant amount of time to print the logs to the consoles; just
because it does cond_resched() after every call_console_drivers().
> I am looking forward to have the console printing offloaded
> into the workqueues. Then printk() will become consistently
> "fast" operation and will cause less surprises like this.
I'm all for it. I need this rework badly. If Jan is too busy at
the moment, which I surely can understand, then I'll be happy to
help ("pick up the patches". please, don't get me wrong).
-ss
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next prev parent reply other threads:[~2016-03-02 14:36 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-03-02 12:01 How to avoid printk() delay caused by cond_resched() ? Tetsuo Handa
2016-03-02 13:38 ` Petr Mladek
2016-03-02 14:11 ` Tetsuo Handa
2016-03-02 15:21 ` Petr Mladek
2016-03-02 14:34 ` Sergey Senozhatsky [this message]
2016-03-02 14:56 ` Petr Mladek
2016-03-02 16:04 ` Jan Kara
2016-03-03 5:41 ` Sergey Senozhatsky
2016-03-02 14:04 ` Sergey Senozhatsky
2016-03-02 15:02 ` Tetsuo Handa
2016-03-02 15:29 ` Sergey Senozhatsky
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