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Date: Thu, 6 Dec 2001 09:10:15 -0500
From: Arjan van de Ven <arjanv@redhat.com>
To: Ravikiran G Thirumalai <kiran@in.ibm.com>
Cc: Arjan van de Ven <arjanv@redhat.com>, linux-kernel@vger.kernel.org,
        lse-tech@lists.sourceforge.net
Subject: Re: [Lse-tech] [RFC] [PATCH] Scalable Statistics Counters
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In-Reply-To: <20011206193940.F20583@in.ibm.com>; from kiran@in.ibm.com on Thu, Dec 06, 2001 at 07:39:40PM +0530
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On Thu, Dec 06, 2001 at 07:39:40PM +0530, Ravikiran G Thirumalai wrote:
> Well, as I mentioned in my earlier post, we have performed 
> "micro benchmarking", which does not reflect the actual run time
> kernel conditions. I guess u gotta take these results with a 
> pinch of salt.  
> 
> But, you cannot deny that there r gonna be a lot of cacheline 
> invalidations, if you use a global counter.  Using per-cpu versions is
> definitely going to improve kernel performance.

there's not that many counters in fact. And if you care about a gige
counter, just bind the card to a specific CPU and you have ad-hoc per-cpu
counters...

The extra cost of getting to them (extra indirection) makes each access 
more expensive..... in the end it might be a loss.

There's several things where per cpu data is useful; low frequency
statistics is not one of them in my opinion. 

Greetings,
   Arjan van de Ven
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