linux-kernel - Re: [PATCH v12 0/3] printk: Make printk() completely async

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Date:	Wed, 13 Jul 2016 13:19:58 +0200
From:	Petr Mladek <pmladek@...e.com>
To:	Viresh Kumar <viresh.kumar@...aro.org>
Cc:	Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jan Kara <jack@...e.com>, Tejun Heo <tj@...nel.org>,
	Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Byungchul Park <byungchul.park@....com>,
	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Subject: Re: [PATCH v12 0/3] printk: Make printk() completely async

On Tue 2016-07-12 10:04:59, Viresh Kumar wrote:
> On 12-07-16, 17:59, Petr Mladek wrote:
> > On Mon 2016-07-11 12:25:11, Viresh Kumar wrote:
> > > We were also screwed because of the problem this thread is trying to solve,
> > > which I posted last week [1].
> > > 
> > > And then I found this thread which fixed my issue, thanks a lot guys :)
> > > 
> > > Tested-by: Viresh Kumar <viresh.kumar@...aro.org>
> > > 
> > > Though, I would also like to mention one unwanted thing that happened on
> > > my setup :)
> > > 
> > > [   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.
> 
> Sorry got confused a bit here..
> 
> Which patch are you taking about here ? As you replied below my
> message, I believe that you are talking about the 3 patches that were
> posted in this series. But the rest of your comment looks like the
> fourth fixup patch that Sergey shared :)

You are right. I was talking about the 4th patch. It was sent as
another reply to this mail. I thought the 4th patch solved your
problems with missing messages during the suspend. 
 
> So, the fixup patch doesn't fix any issues in my case, to make it
> clear. I still have my system hanging somewhere.

I see. Thanks for clarification and I am sorry for the confusion.

Best Regards,
Petr