linux-kernel - Re: [Regression] 2.6.24-git3: Major annoyance during suspend/hibernation on x86-64 (bisected)

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Date:	Mon, 28 Jan 2008 02:26:21 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Steven Rostedt <srostedt@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Dmitry Adamushko <dmitry.adamushko@...il.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [Regression] 2.6.24-git3: Major annoyance during suspend/hibernation on x86-64 (bisected)

On Sunday, 27 of January 2008, Ingo Molnar wrote:
> 
> * Rafael J. Wysocki <rjw@...k.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@...hat.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@...e.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.

Thanks,
Rafael
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