linux-kernel - Make RCU tree CPU topology aware?

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Message-ID: <20150817103931.GB4588@agordeev.usersys.redhat.com>
Date:	Mon, 17 Aug 2015 11:39:34 +0100
From:	Alexander Gordeev <agordeev@...hat.com>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Make RCU tree CPU topology aware?

Hi Paul,

Currently RCU tree distributes CPUs to leafs based on consequent CPU
IDs. That means CPUs from remote caches and even nodes might end up
in the same leaf.

I did not research the impact, but at the glance that seems at least
sub-optimal; especially in case of remote nodes, when CPUs access
each others' memory?

I am thinking of topology-aware RCU geometry where the RCU tree reflects
the actual system topology. I.e by borrowing it from schedulling domains
or soemthing like that.

Do you think it worth the effort to research this question or I am
missing something and the current access patterns are just optimal?

Thanks!

-- 
Regards,
Alexander Gordeev
agordeev@...hat.com
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