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Date: Wed, 04 Apr 2007 07:29:01 +0200
From: Eric Dumazet <dada1@cosmosbay.com>
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To: "H. Peter Anvin" <hpa@zytor.com>
CC: Jeremy Fitzhardinge <jeremy@goop.org>, Ulrich Drepper <drepper@redhat.com>,
       Davide Libenzi <davidel@xmailserver.org>,
       Linux Kernel <linux-kernel@vger.kernel.org>,
       Andrew Morton <akpm@linux-foundation.org>, Andi Kleen <ak@suse.de>
Subject: Re: getting processor numbers
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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.