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Message-Id: <1194513081.6289.130.camel@twins>
Date: Thu, 08 Nov 2007 10:11:21 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Matt Mackall <mpm@...enic.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
Marin Mitov <mitov@...p.bas.bg>, linux-kernel@...r.kernel.org,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...e.hu>, Andi Kleen <ak@...e.de>
Subject: Re: is minimum udelay() not respected in preemptible SMP
kernel-2.6.23?
On Wed, 2007-11-07 at 18:20 -0600, Matt Mackall wrote:
> This and other cases
> (lots of per_cpu users, IIRC) actually want a migrate_disable() which
> is a proper subset.
The disadvantage of migrate_disable() is that it complicates the
load-balancer but more importantly, that it does bring a form of
latencies with it that are hard to measure. Using preempt_disable() for
these current per-cpu users basically forces them to keep it short.
Which is a GOOD (tm) thing.
If we go overboard with this migrate_disable() stuff we can end up with
a very hard to analyse system that sporadically does weird stuff.
So, please, don't start that again.
Also see:
http://lkml.org/lkml/2007/7/23/338
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