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: <475EACB8.7080608@keyaccess.nl>
Date:	Tue, 11 Dec 2007 16:28:56 +0100
From:	Rene Herman <rene.herman@...access.nl>
To:	Paul Rolland <rol@...917.net>
CC:	David Newall <david@...idnewall.com>,
	"H. Peter Anvin" <hpa@...or.com>, Krzysztof Halasa <khc@...waw.pl>,
	Pavel Machek <pavel@....cz>, Andi Kleen <andi@...stfloor.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	"David P. Reed" <dpreed@...d.com>, linux-kernel@...r.kernel.org,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, rol@...be.net
Subject: Re: RFC: outb 0x80 in inb_p, outb_p harmful on some modern AMD64
 with MCP51 laptops

On 11-12-07 15:15, Rene Herman wrote:

> On 11-12-07 14:32, Paul Rolland wrote:
> 
>>> On 11-12-07 13:08, David Newall wrote:
>>>
>>>> Rene Herman wrote:
>>
>>> (*) some local testing shows it to be almost exactly that for both 
>>> out and in on my own PC -- a little over. If anyone cares, see 
>>> attached little test program. The "little over" I don't worry about. 
>>> 0 us delay is also fine for me and if any code was _that_ fragile it 
>>> would have broken long ago.
>>
>> Some results :
> 
> Okay, these vary to wildly for you and might I suppose be a serialising 
> artifact or some such. Give me a bit and I'll try to improve it...

This might be a bit more constant, I suppose. This serialises with cpuid. 
Don't see a difference locally, but perhaps you do.

On a Duron 1300 with an actual ISA bus, "out" is between 1300 and 1600 for 
me and "in" between 1200 and 1500 with a few flukes above that which will I 
suppose be caused by the bus (ISA _or_ PCI) being momentarily busy or some 
such...

Rene.

View attachment "port80.c" of type "text/plain" (1680 bytes)