linux-kernel - Re: RFC: outb 0x80 in inb_p, outb_p harmful on some modern AMD64 with MCP51 laptops

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Message-ID: <20071207171957.73b619b1@the-village.bc.nu>
Date:	Fri, 7 Dec 2007 17:19:57 +0000
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Andi Kleen <andi@...stfloor.org>,
	"David P. Reed" <dpreed@...d.com>, linux-kernel@...r.kernel.org,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: RFC: outb 0x80 in inb_p, outb_p harmful on some modern AMD64
 with MCP51 laptops

On Fri, 7 Dec 2007 17:31:16 +0100
Andi Kleen <andi@...stfloor.org> wrote:

> > You don't need to. Port 0x80 historically is about 8uS so just udelay(8)
> > and make sure the initial default delay is conservative enough before the
> 
> How would you make it conservative enough handling let's say a 6Ghz CPU
> that can execute multiple jumps per cycle?

Pick a sane worst case and go with it at boot. We don't have to be
accurate before we tune udelay - over long in uSecs isnt going to hurt,
and most post boot _p's can be replaced by udelay(8) now

Alan
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