Re: [PATCH 1/2] Make the batch size of the percpu_counterconfigurable

From: Tim Chen
Date: Tue Apr 30 2013 - 15:01:10 EST

On Tue, 2013-04-30 at 18:27 +0000, Christoph Lameter wrote:
> On Tue, 30 Apr 2013, Tim Chen wrote:
> > > But you will have to dereference the pointer whenever you want the batch
> > > size from the hot path. Looks like it would be better to put the value
> > > there directly. You have a list of percpu counters that can be traversed
> > > to change the batch size.
> > >
> >
> > I have considered that. But the list is not available unless we have
> > CONFIG_HOTPLUG_CPU compiled in.
> percpu counters are performance sensitive and with the pointer you
> will need to reference another one increasing the cache footprint. You are
> touching an additional cacheline somewhere in memory frequently. Not good.

Seems like there's objection to make batch a pointer and I'll have to
store its value in per cpu pointer.

Will it be acceptable if I make the per cpu counter list under
CONFIG_CPU_HOTPLUG default? I will need the list to go through all
counters to update the batch value sizes. The alternative will be to
make the configurable batch option only available under

Which is the preferable approach or there are other clever alternatives?


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