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Date: Fri, 7 Dec 2001 01:05:58 +0530
From: Dipankar Sarma <dipankar@in.ibm.com>
To: Arjan van de Ven <arjanv@redhat.com>
Cc: Ravikiran G Thirumalai <kiran@in.ibm.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: <20011206091015.B16763@devserv.devel.redhat.com>; from arjanv@redhat.com on Thu, Dec 06, 2001 at 09:10:15AM -0500
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On Thu, Dec 06, 2001 at 09:10:15AM -0500, Arjan van de Ven wrote:
> On Thu, Dec 06, 2001 at 07:39:40PM +0530, Ravikiran G Thirumalai wrote:
> > 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.

If it is a low frequency statistics then the expensive access wouldn't 
really matter much, right ? On the other hand, this will likely help 
specially with larger number of CPUs.

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

It is quite possible that you are right. What we need to do is
a measurement effort to understand the impact.

Thanks
Dipankar
-- 
Dipankar Sarma  <dipankar@in.ibm.com> http://lse.sourceforge.net
Linux Technology Center, IBM Software Lab, Bangalore, India.
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