linux-kernel - Re: [RFT] Port 0x80 I/O speed

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Date:	Wed, 12 Dec 2007 13:07:47 +1100
From:	Nigel Cunningham <nigel@...el.suspend2.net>
To:	Rene Herman <rene.herman@...il.com>
CC:	Linux Kernel <linux-kernel@...r.kernel.org>, dpreed@...d.com,
	Alan Cox <alan@...rguk.ukuu.org.uk>, pavel@....cz,
	andi@...stfloor.org, rol@...917.net,
	Krzysztof Halasa <khc@...waw.pl>, david@...idnewall.com,
	hpa@...or.com, john@...ffel.org, linux-os@...logic.com
Subject: Re: [RFT] Port 0x80 I/O speed

Rene Herman wrote:
> On 12-12-07 00:55, Nigel Cunningham wrote:
> 
>> (AMD 1.8GHz Turion, running at 800MHz. ATI RS480 - Mitac 8350 mobo)
>>
>> nigel@...e:~/Downloads$ gcc port80.c -o port80
>> nigel@...e:~/Downloads$ sudo ./port80
>> cycles: out 1235, in 1207
> 
> Looking good.
> 
>> nigel@...e:~/Downloads$ gcc -O2 port80.c -o port80
>> nigel@...e:~/Downloads$ sudo ./port80
>> cycles: out 1844674407370794, in 1844674407369408
> 
> Obviously not. I suppose this changes with -m32 on the GCC command line?
> (sorry for missing that, I have no 64-bit machines).

Yes, it does:

nigel@...e:~/Downloads$ gcc -m32 -o port80 port80.c
nigel@...e:~/Downloads$ sudo ./port80
cycles: out 1231, in 1208
nigel@...e:~/Downloads$ sudo ./port80
cycles: out 1233, in 1210

Incidentally:

nigel@...e:~/Downloads$ processor_speed

(A little script I made because my lappy does a solid lock every now and
then that seems to be cpu-freq related - locking it to one frequency
makes the lock far less common).

Speed is now 1800000.
nigel@...e:~/Downloads$ sudo ./port80
cycles: out 2472, in 2505
nigel@...e:~/Downloads$ sudo ./port80
cycles: out 2489, in 2515
nigel@...e:~/Downloads$ sudo ./port80
cycles: out 2481, in 2503
nigel@...e:~/Downloads$ sudo ./port80
cycles: out 2476, in 2507

So the same effect Maxim reported is seen here.

Regards,

Nigel
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