linux-kernel - Re: [PATCH 9/11] Panic delay fix

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Message-ID: <20070215101713.GK26240@elf.ucw.cz>
Date:	Thu, 15 Feb 2007 11:17:13 +0100
From:	Pavel Machek <pavel@....cz>
To:	Zachary Amsden <zach@...are.com>
Cc:	Alan <alan@...rguk.ukuu.org.uk>,
	Rusty Russell <rusty@...tcorp.com.au>, Andi Kleen <ak@....de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...l.org>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Chris Wright <chrisw@...s-sol.org>
Subject: Re: [PATCH 9/11] Panic delay fix

Hi!

> >>We'd have to audit and figure out what udelays are for hardware and
> >>which are not, but the evidence is that the vast majority of them are
> >>for hardware and not needed for virtualization.
> >>    
> >
> >Which is irrelevant since the hardware drivers won't be used in a
> >virtualised environment with any kind of performance optimisation.
> >  
> 
> Which is why an audit is irrelevant for the most part.  Note on the 
> performance below.

You know it is ugly. Alan demonstrated it even hurts performance, but
being ugly is the main problem.

If you _need_ to avoid udelay() in some cases, introduce
udelay_unless_virtualized(), and switch few users to it. Just globaly
defining udelay to nop is _ugly_.
								Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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