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: <475EB263.2050405@keyaccess.nl>
Date:	Tue, 11 Dec 2007 16:53:07 +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 16:37, Paul Rolland wrote:

Great, thanks for the quick replies.

That last one below especially is quite a bit more than 1. As said before, 
most hardware isn't in fact going to need anything but I suppose udelay(2) 
might be the "safer" replacement for the outb then...

> On Tue, 11 Dec 2007 16:28:56 +0100
> Rene Herman <rene.herman@...access.nl> wrote:
> 
>> On 11-12-07 15:15, Rene Herman wrote:
>>
>>> On 11-12-07 14:32, Paul Rolland wrote:
>>>
>> This might be a bit more constant, I suppose. This serialises with cpuid. 
>> Don't see a difference locally, but perhaps you do.
> Well, yes, at least on the PIII and the Opteron... Core2 is still changing
> a lot...
> 
>> 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...

> The results :
> 
> Core 2Duo 1.73 GHz :
> [root@tux tmp]# ./in2
> out: 2777
> in : 2519
> [root@tux tmp]# ./in2
> out: 2440
> in : 2391
> [root@tux tmp]# ./in2
> out: 2460
> in : 2388

Okayish I guess, especially when subsequent runs stay near those values.

2500/1730 = 1.45 us

> Pentium III :
> [root@...-dev /tmp]# ./in2
> out: 746
> in : 747
> [root@...-dev /tmp]# ./in2
> out: 746
> in : 747
> [root@...-dev /tmp]# ./in2
> out: 746
> in : 745

746/600 ~= 1.24 us

> AMD Opteron 150 :
> -bash-3.1# ./in2
> out: 4846
> in : 4845
> -bash-3.1# ./in2
> out: 4846
> in : 4846
> -bash-3.1# ./in2
> out: 4846
> in : 4845

4846 / 2400 = 2.02 us

Rene.

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