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Subject: Re: [Regression] 2.6.24-git3: Major annoyance during
	suspend/hibernation on x86-64 (bisected)
From: Peter Zijlstra <a.p.zijlstra@chello.nl>
To: "Rafael J. Wysocki" <rjw@sisk.pl>
Cc: Ingo Molnar <mingo@elte.hu>, Steven Rostedt <srostedt@redhat.com>,
       Andrew Morton <akpm@linux-foundation.org>,
       Linus Torvalds <torvalds@linux-foundation.org>,
       LKML <linux-kernel@vger.kernel.org>,
       Dmitry Adamushko <dmitry.adamushko@gmail.com>
In-Reply-To: <200801280226.22013.rjw@sisk.pl>
References: <200801272229.48955.rjw@sisk.pl> <20080127215904.GB2686@elte.hu>
	 <200801280226.22013.rjw@sisk.pl>
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Date: Thu, 31 Jan 2008 16:58:48 +0100
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On Mon, 2008-01-28 at 02:26 +0100, Rafael J. Wysocki wrote:
> On Sunday, 27 of January 2008, Ingo Molnar wrote:
> > 
> > * Rafael J. Wysocki <rjw@sisk.pl> wrote:
> > 
> > > Hi,
> > > 
> > > 2.6.24-git3 adds a 5 - 10 sec delay to the suspend and hibernation 
> > > code paths (probably related to the disabling of nonboot CPUs), which 
> > > is !@#$%^&*() annoying.
> > > 
> > > It's 100% reproducible on my HP nx6325 and bisection idendified the 
> > > following commit as the first bad one:
> > > 
> > > commit 764a9d6fe4b52995c8aba277e3634385699354f4
> > > Author: Steven Rostedt <srostedt@redhat.com>
> > > Date:   Fri Jan 25 21:08:04 2008 +0100
> > > 
> > >     sched: track highest prio task queued
> > 
> > hm, this patch is a NOP, so it's weird that it has an effect.
> > 
> > Do you have serial logging enabled perhaps? If the following WARN_ON() 
> > triggers:
> > 
> > +               WARN_ON(p->prio < rq->rt.highest_prio);
> > 
> > then perhaps that can cause a 5-10 seconds delay. (that's how much time 
> > it takes to printk a warning on the slowest serial settings)
> > 
> > but if you use suspend, then any such printks would be preserved in the 
> > dmesg, right? If the WARN_ON() triggers, and if you remove it, do things 
> > get faster?
> 
> No, this isn't the WARN_ON().
> 
> > this does have the feel of being scheduling related, but are you 
> > absolutely sure about the precise identity of the patch?
> 
> Actually, not quite.  That's why I have verified it and found that another
> patch is really responsible for the issue, namely:
> 
> commit 82a1fcb90287052aabfa235e7ffc693ea003fe69
> Author: Ingo Molnar <mingo@elte.hu>
> Date:   Fri Jan 25 21:08:02 2008 +0100
> 
>     softlockup: automatically detect hung TASK_UNINTERRUPTIBLE tasks
> 
> Reverting this commit (it reverts with some minor modifications) fixes the
> problem for me.

I can seem to reproduce this:

[root@opteron cpu1]# time echo 0 > online

real    0m6.230s
user    0m0.000s
sys     0m0.010s
[root@opteron cpu1]# echo 1 > online
[root@opteron cpu1]# time echo 0 > online

real    0m7.966s
user    0m0.000s
sys     0m0.011s


I'll have a look at it.