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Date: Fri, 7 Dec 2001 15:40:17 +0530
From: Dipankar Sarma <dipankar@in.ibm.com>
To: Niels Christiansen <nchr@us.ibm.com>
Cc: kiran@linux.ibm.com, lse-tech@lists.sourceforge.net,
        linux-kernel@vger.kernel.org
Subject: Re: [Lse-tech] [RFC] [PATCH] Scalable Statistics Counters
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In-Reply-To: <OFEDC68CF2.34B05314-ON85256B1B.00355B4C@raleigh.ibm.com>; from nchr@us.ibm.com on Fri, Dec 07, 2001 at 04:52:40AM -0500
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On Fri, Dec 07, 2001 at 04:52:40AM -0500, Niels Christiansen wrote:
> 
> Hello Dikanpar,
> | It should be easy to place the counters in appropriately close
> | memory if linux gets good NUMA APIs built on top of the topology
> | services. If we extend kmem_cache_alloc() to allocate memory
> | in a particular NUMA node, we could simply do this for placing the
> | counters -
> | ...
> | This would put the block of counters corresponding to a CPU in
> | memory local to the NUMA node. If there are more sophisticated
> | APIs available for suitable memory selection, those too can be made
> | use of here.
> |
> | Is this the kind of thing you are looking at ?
> 
> I'm no NUMA person so I can't verify your code snippet but if it does
> what you say, yes, that is exactly what I meant:  We may have to deal
> with both cache coherence and placement of counters in local memory.

Yes, we will likely need to place the conters in memory closest to
the corresponding CPUs.

I haven't yet started looking at the current NUMA proposals, but
I hope that there will be support for NUMA-aware allocations. The
flexible allocator scheme in our statctr implementation allows
each counter block corresponding to a CPU to be allocated separately
and we can make the locational judgement at that time as indicated
in my hypothetical changes to the statctr code snippet.

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