linux-kernel - Re: [PATCH] scheduler: fix x86 regression in native_sched

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Date:	Sat, 8 Dec 2007 16:33:27 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Michael Buesch <mb@...sch.de>
Cc:	Mark Lord <lkml@....ca>, Guillaume Chazarain <guichaz@...oo.fr>,
	stefano.brivio@...imi.it, Nick Piggin <nickpiggin@...oo.com.au>,
	Robert Love <rml@...h9.net>, linux-kernel@...r.kernel.org,
	Dave Jones <davej@...hat.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Len Brown <lenb@...nel.org>
Subject: Re: [PATCH] scheduler: fix x86 regression in native_sched_clock


* Michael Buesch <mb@...sch.de> wrote:

> On Saturday 08 December 2007 16:13:41 Ingo Molnar wrote:
> > 
> > * Mark Lord <lkml@....ca> wrote:
> > 
> > > Ingo Molnar wrote:
> > >> ...
> > >> thanks. I do get the impression that most of this can/should wait until 
> > >> 2.6.25. The patches look quite dangerous.
> > > ..
> > >
> > > I confess to not really trying hard to understand everything in this 
> > > thread, but the implication seems to be that this bug might affect 
> > > udelay() and possibly jiffies ?
> > 
> > no, it cannot affect jiffies. (jiffies was a red herring all along)
> > 
> > udelay() cannot be affected either - sched_clock() has no effect on 
> > udelay(). _But_, when there are TSC problems then tsc based udelay() 
> > suffers too so the phenomenons may _seem_ related.
> 
> What about msleep()? I suspect problems in b43 because of this issue. 
> msleep() returning too early. Is that possible with this bug?

i cannot see how. You can verify msleep by running something like this:

  while :; do time usleep 111000; done

you should see a steady stream of:

 real    0m0.113s
 real    0m0.113s
 real    0m0.113s

(on an idle system). If it fluctuates, with occasional longer delays, 
there's some timer problem present.

	Ingo
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