linux-kernel - Re: [PATCH] printk: git rid of [sched_delayed] message for printk

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Date:	Wed, 24 Sep 2014 13:01:01 +0200
From:	Jan Kara <jack@...e.cz>
To:	Markus Trippelsdorf <markus@...ppelsdorf.de>
Cc:	Jan Kara <jack@...e.cz>, Steven Rostedt <rostedt@...dmis.org>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] printk: git rid of [sched_delayed] message for
 printk_deferred

On Sat 20-09-14 17:47:33, Peter Zijlstra wrote:
> On Sat, Sep 20, 2014 at 07:12:24AM +0200, Jan Kara wrote:
> > On Thu 18-09-14 19:34:14, Peter Zijlstra wrote:
> > > On Wed, Sep 17, 2014 at 08:31:35PM -0400, Steven Rostedt wrote:
> > > > I totally didn't get what you wrote.
> > > 
> > > :-)
> > > 
> > > > We don't want to know if it got delayed, then the patch to remove that
> > > > print seems correct.
> > > 
> > > Why would you not want to know that? Also was that the actual argument?
> > > Lemme go check the earlier emails -- I cannot find that argument in the
> > > first few emails.
> >   Well, so what gets delayed is printing from kernel buffer to console.
> > So this is the same as when you do printk() when console lock is taken by
> > someone else. So it seems a bit strange to prepend [delayed] in some cases
> > and not in others.
> 
> The difference is that when someone else has the console lock, he
> guarantees it gets out. Whereas with the delayed thing it can take a
> virtual forever to get out.
> 
> > Another question is what the [delayed] prefix would be useful for? If the
> > message eventually gets printed to console I don't see why you would care
> > it was printed few ms after it entered the kernel buffer (after all the
> > time stamp before the line will be the time when it entered the kernel
> > buffer). And if the kernel crashes in such a way that the message doesn't
> > get printed, then bad luck but prefix in the kernel log buffer isn't going
> > to make that any better :)
> > 
> > This all feels like bikeshedding, I don't deeply care what gets done but I
> > wanted to point out I don't really see a use for [delayed]...
> 
> Sure, I was just pointing out that those arguments had not been made. I
> think you're right, if you see the msg it obviously made it out. If you
> don't see it, you don't know either way.
> 
> But a patch removing it _must_ make those arguments, it did not.
  Markus, could you please resend the patch with Steven's ack and expanded
changelog? Thanks!

								Honza
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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