Re: [Lse-tech] [RFC] [PATCH] Scalable Statistics Counters

Ravikiran G Thirumalai (kiran@in.ibm.com)
Thu, 6 Dec 2001 19:39:40 +0530

On Thu, Dec 06, 2001 at 01:07:37PM +0000, Arjan van de Ven wrote:
> >
> > >
> > > How many and which counters were converted for the test you refer to?
> > >
> >
> > Well, I wrote a simple kernel module which just increments a shared global
> > counter a million times per processor in parallel, and compared it with
> > the statctr which would be incremented a million times per processor in
> > parallel..
>
> Would you care to point out a statistic in the kernel that is
> incremented
> more than 10.000 times/second ? (I'm giving you a a factor of 100 of
> playroom
> here) [One that isn't per-cpu yet of course]

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.

Kiran

-- 
Ravikiran G Thirumalai <kiran@in.ibm.com>
Linux Technology Center, IBM Software Labs,
Bangalore.
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