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Date: Sat, 23 Feb 2002 14:01:07 -0600
From: Stephen Lord <lord@sgi.com>
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To: Andrew Morton <akpm@zip.com.au>
CC: Robert Love <rml@tech9.net>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] only irq-safe atomic ops
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Andrew Morton wrote:

>Robert Love wrote:
>
>>...
>>
>>Question: if (from below) you are going to use atomic operations, why
>>make it per-CPU at all?  Just have one counter and atomic_inc and
>>atomic_read it.  You won't need a spin lock.
>>
>
>Oh that works fine.   But then it's a global counter, so each time
>a CPU marks a page dirty, the counter needs to be pulled out of
>another CPU's cache.   Which is not a thing I *need* to do.
>
>As I said, it's a micro-issue.  But it's a requirement which 
>may pop up elsewhere.
> 
>
I can tell you that Irix has just such a global counter for the amount of
delayed allocate pages - and it gets to be a major point of cache contention
once you get to larger cpu counts. So avoiding that from the start would
be good.

Steve



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