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Message-ID: <43BF3355.5060606@yahoo.com.au>
Date: Sat, 07 Jan 2006 14:19:49 +1100
From: Nick Piggin <nickpiggin@yahoo.com.au>
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To: Andi Kleen <ak@suse.de>
CC: Andrew Morton <akpm@osdl.org>, Benjamin LaHaise <bcrl@kvack.org>,
       linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH] use local_t for page statistics
References: <20060106215332.GH8979@kvack.org> <20060106163313.38c08e37.akpm@osdl.org> <43BF2D03.2030908@yahoo.com.au> <200601070401.47618.ak@suse.de>
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Andi Kleen wrote:
> On Saturday 07 January 2006 03:52, Nick Piggin wrote:
> 
> 
>>No. On many load/store architectures there is no good way to do local_t,
>>so something like ppc32 or ia64 just uses all atomic operations for
> 
> 
> well, they're just broken and need to be fixed to not do that.
> 

How?

> Also I bet with some tricks a seqlock like setup could be made to work.
> 

I asked you how before. If you can come up with a way then it indeed
might be a good solution... The problem I see with seqlock is that it
is only fast in the read path. That path is not the issue here.

> 
>>local_t, and ppc64 uses 3 counters per-cpu thus tripling the cache
>>footprint.
> 
> 
> and ppc64 has big caches so this also shouldn't be a problem.
> 

Well it is even less of a problem for them now, by about 1/3.

Performance-wise there is really no benefit for even i386 or x86-64
to move to local_t now either so I don't see what the fuss is about.

-- 
SUSE Labs, Novell Inc.

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