linux-kernel - Re: [PATCH] x86: enable preemption in delay

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Message-ID: <20080525122808.54f5026e@infradead.org>
Date:	Sun, 25 May 2008 12:28:08 -0700
From:	Arjan van de Ven <arjan@...radead.org>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-rt-users <linux-rt-users@...r.kernel.org>, akpm@...l.org,
	Ingo Molnar <mingo@...e.hu>,
	Clark Williams <clark.williams@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	"Luis Claudio R. Goncalves" <lclaudio@...g.org>,
	Gregory Haskins <ghaskins@...ell.com>, Andi Kleen <ak@...e.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH] x86: enable preemption in delay

On Sun, 25 May 2008 21:01:32 +0200 (CEST)
Thomas Gleixner <tglx@...utronix.de> wrote:

> On Sun, 25 May 2008, Arjan van de Ven wrote:
> 
> > On Sat, 24 May 2008 23:11:20 -0400 (EDT)
> > Steven Rostedt <rostedt@...dmis.org> wrote:
> > > 
> > > In git commit 35d5d08a085c56f153458c3f5d8ce24123617faf, Andrew
> > > Morton placed preempt_disable around the entire delay due to
> > > TSC's not working nicely on SMP.  Unfortunately for those that
> > > care about latencies this is devastating! Especially when we have
> > > callers to mdelay(8).
> > 
> > we used to have a WARN_ON if mdelay was called while preemptable..
> > maybe we should put that back in?
> 
> We'd better have one which warns, when mdelay is called with
> preemption disabled.

argument for my variant was "should have used msleep instead"...

I don't disagree that mdelay() is harmful in general; at some point I
stuck a WARN_ON in mdelay when called from irq context...
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