linux-kernel - Re: getting processor numbers

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Date:	Wed, 04 Apr 2007 07:29:01 +0200
From:	Eric Dumazet <dada1@...mosbay.com>
To:	"H. Peter Anvin" <hpa@...or.com>
CC:	Jeremy Fitzhardinge <jeremy@...p.org>,
	Ulrich Drepper <drepper@...hat.com>,
	Davide Libenzi <davidel@...ilserver.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andi Kleen <ak@...e.de>
Subject: Re: getting processor numbers

H. Peter Anvin a écrit :
> Eric Dumazet wrote:
>>
>> There is one thing that always worried me.
>>
>> Intel & AMD manuals make clear that mixing data and program in the 
>> same page is bad for performance.
>>
>> In particular, x86_64 vsyscall put jiffies and other 
>> vsyscall_gtod_data_t right in the midle of code. That is certainly not 
>> wise.
>>
>> A probably sane implementation should use two pages, one for code, one 
>> for data.
>>
> 
> Mutable data should be separated from code.  I think any current CPU 
> will do fine as long as they are in separate 128-byte chunks, but they 
> need at least that much separation.
> 
> Readonly data does not need to be separated from code.
> 

Yes... jiffies & vsyscall_gtod_data_t is writen HZ times per second.

Not really readonly I'm afraid.


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