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

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Message-ID: <alpine.LFD.1.10.0805252217580.3295@apollo.tec.linutronix.de>
Date:	Sun, 25 May 2008 22:21:51 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Steven Rostedt <rostedt@...dmis.org>
cc:	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, Steven Rostedt wrote:
> 
> On Sun, 25 May 2008, Thomas Gleixner wrote:
> >
> > +/*
> > + * 5 usec on a 1GHZ machine. Not necessarily correct, but not too long
> > + * either.
> 
> And what happens when we have 10GHz boxes that can do migration in 1us,
> and the delay that is asked for is 2us. We can return early.  I don't like
> to place assumptions of this kind that can hurt with future hardware
> enhancements.

Do the math. It's 500ns on a 10GHz machine then. So nothing to worry
about and future proof. 

Also when those 10GHZ machines arrive the synchronized TSC should have
finally become reality.

Thanks,

	tglx
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