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

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Message-ID: <20070215003339.1420faff@localhost.localdomain>
Date:	Thu, 15 Feb 2007 00:33:39 +0000
From:	Alan <alan@...rguk.ukuu.org.uk>
To:	Zachary Amsden <zach@...are.com>
Cc:	Rusty Russell <rusty@...tcorp.com.au>, Pavel Machek <pavel@....cz>,
	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

On Wed, 14 Feb 2007 13:53:08 -0800
Zachary Amsden <zach@...are.com> wrote:

> > IDE on several platforms has performance critical paths that use
> > ndelay(400) or failing that udelay(1)
> 
> Ok, I buy that.  A 486DX / 33 Mhz processor takes 10 cycles to issue a 
> CALL / RET pair.  This is about 300ns.  Is there an issue with being too 
> early to issue I/O operations or too late?

Too early you lose, too late you just waste clock time.

> But I fail to see how such careful timing can be done at this 
> granularity on such hardware without well tweaked assembly code. 

Thats what is used  most platforms use udelay(1) in fact however
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