linux-kernel - Re: x86: clean up smpboot.c's use of udelay+schedule

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Message-ID: <20120131053236.3f120f11@infradead.org>
Date:	Tue, 31 Jan 2012 05:32:36 -0800
From:	Arjan van de Ven <arjan@...radead.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	linux-kernel@...r.kernel.org, x86@...nel.org,
	arjanvandeven@...il.com, Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: x86: clean up smpboot.c's use of udelay+schedule

On Tue, 31 Jan 2012 13:43:41 +0100
Ingo Molnar <mingo@...e.hu> wrote:
> > +			usleep_range(100, 200);
> 
> I'm wondering whether we could shorten this delay to say 10 
> usecs and thus save 0.1 msecs (or more) from a typical SMP 
> bootup?

doesn't matter really; bringing up a cpu is several orders more
expensive (> 100msec in 3.2, in 3.3 this got optimized to maybe 30 msec)
0.1 msec is the least of anyone's worries at this point ;-)

(would be nice if this was a completion, but this is rather fragile
code in general... at least not making it spin is an incremental
improvement)

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