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

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Message-ID: <20071208151341.GA25413@elte.hu>
Date:	Sat, 8 Dec 2007 16:13:41 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Mark Lord <lkml@....ca>
Cc:	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>, Michael Buesch <mb@...sch.de>,
	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


* 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.

> If so, then fixing it has to be a *must* for 2.6.24, as otherwise 
> we'll get all sorts of one-in-while odd driver bugs.. like maybe these 
> two for starters:
>
> [Bug 9492] 2.6.24:  false double-clicks from USB mouse
> [Bug 9489] 20000+ wake-ups/second in 2.6.24

iirc these high rate wakeups happened on 2.6.22 too.

	Ingo
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