From: Matt Mackall <mpm@selenic.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Marin Mitov <mitov@issp.bas.bg>,
linux-kernel@vger.kernel.org,
Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@elte.hu>,
Andi Kleen <ak@suse.de>
Subject: Re: is minimum udelay() not respected in preemptible SMP kernel-2.6.23?
Date: Wed, 7 Nov 2007 18:20:27 -0600 [thread overview]
Message-ID: <20071108002027.GV17536@waste.org> (raw)
In-Reply-To: <20071107123045.c6d4b855.akpm@linux-foundation.org>
On Wed, Nov 07, 2007 at 12:30:45PM -0800, Andrew Morton wrote:
> Ow. Yes, from my reading delay_tsc() can return early (or after
> heat-death-of-the-universe) if the TSCs are offset and if preemption
> migrates the calling task between CPUs.
>
> I suppose a lameo fix would be to disable preemption in delay_tsc().
preempt_disable is lousy documentation here. This and other cases
(lots of per_cpu users, IIRC) actually want a migrate_disable() which
is a proper subset. We can simply implement migrate_disable() as
preempt_disable() for now and come back later and implement a proper
migrate_disable() that still allows preemption (and thus avoids the
latency).
--
Mathematics is the supreme nostalgia of our time.
next prev parent reply other threads:[~2007-11-08 0:22 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-11-07 17:21 is minimum udelay() not respected in preemptible SMP kernel-2.6.23? Marin Mitov
2007-11-07 20:30 ` Andrew Morton
2007-11-07 23:10 ` Andi Kleen
2007-11-08 0:20 ` Matt Mackall [this message]
2007-11-08 0:31 ` Andi Kleen
2007-11-08 1:03 ` Matt Mackall
2007-11-08 1:20 ` Andi Kleen
2007-11-08 2:44 ` Matt Mackall
2007-11-08 11:46 ` Avi Kivity
2007-11-08 15:10 ` Matt Mackall
2007-11-08 9:11 ` Peter Zijlstra
2007-11-08 15:43 ` Matt Mackall
2007-11-08 11:24 ` Marin Mitov
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