Messages in this thread | | | Subject | Re: [PATCH 1/2]percpu: introduce read mostly percpu API | From | Eric Dumazet <> | Date | Wed, 20 Oct 2010 09:53:54 +0200 |
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Le mercredi 20 octobre 2010 à 09:35 +0200, Andi Kleen a écrit : > On Wed, Oct 20, 2010 at 07:18:00AM +0200, Eric Dumazet wrote: > > Le mercredi 20 octobre 2010 à 11:07 +0800, Shaohua Li a écrit : > > > Add a new readmostly percpu section and api, next patch will use it. > > > > > > Signed-off-by: Shaohua Li <shaohua.li@intel.com> > > > --- > > > > > > Could you precisely describe why grouping together read mostly percpu > > variables is a win ? Especially when you add in your next patch a single > > variable ? > > Not Shaohua, but I can explain it: > > There is some per cpu data which is read by other CPUs. In this > case it's a win to use the separate section because you avoid false sharing > and the cache line can be kept in shared mode on all CPUs. > > The next patch has an example of such data: data which is read > by another CPU to send something to the target CPU. > > I think the concept is useful and makes a lot of sense. > The alternative would be __read_mostly NR_CPUS arrays, but > we all know that is a bad idea because it wastes too much memory > on CONFIG_MAX_SMP setups. >
My question was more a rethoric one. I understand for sure the intent.
All this should be explained in changelog, so that people know when/where use this new class of per_cpu variables ;)
Thanks
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