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    SubjectRe: [PATCH 15/15] x86: Fix cpu_coregroup_mask to return correct cpumask on multi-node processors
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    On Thu, 2009-08-27 at 17:25 +0200, Andreas Herrmann wrote:
    > On Tue, Aug 25, 2009 at 11:55:43AM +0200, Peter Zijlstra wrote:
    > > On Tue, 2009-08-25 at 11:31 +0200, Andreas Herrmann wrote:
    > > > On Mon, Aug 24, 2009 at 05:36:16PM +0200, Peter Zijlstra wrote:
    > > > > On Thu, 2009-08-20 at 15:46 +0200, Andreas Herrmann wrote:
    > > > > > The correct mask that describes core-siblings of an processor
    > > > > > is topology_core_cpumask. See topology adapation patches, especially
    > > > > > http://marc.info/?l=linux-kernel&m=124964999608179
    > > > >
    > > > >
    > > > > argh, violence, murder kill.. this is the worst possible hack and you're
    > > > > extending it :/
    > > >
    > > > So this is the third code area
    > > > (besides sched_*_power_savings sysfs interface, and the __cpu_power fiddling)
    > > > that is crap, mess, a hack.
    > > >
    > > > Didn't know that I'd enter such a minefield when touching this code. ;-(
    > >
    > > Yeah, you're lucky that way ;-) Its been creaking for a while, and I've
    > > been making noises to the IBM people (who so far have been the main
    > > source of power saving patches) to clean this up, but now you trod onto
    > > all of it at once..
    > >
    > > > What would be your perferred solution for the
    > > > core_cpumask/llc_shared_map stuff? Another domain level to get rid of
    > > > this function?
    > >
    > > Right, I'd like to see everything exposed as domain levels.
    > >
    > >
    > > numa-cluster
    > > numa
    > > socket
    > > in-socket-numa
    > > multi-core
    > > shared-cache
    > > core
    > > threads
    >
    > Out of curiosity, when does cpu_core_mask differ from llc_shared_map
    > on Intel? Only in case of MCM (e.g. Core2 Quad)?

    Yes, I think both c2q and some dual-core opteron have multiple cache
    domains per socket.

    > If yes, the hackery of cpu_coregroup_mask() could be replace by
    > the domain that I'd like to introduce for Magny-Cours:
    >
    > MC domain span would represent one die.
    > The new domain would span all dies in an MCM.
    >
    > Bad idea?

    No, I think all the mentioned chips have the multi-die thing in common,
    the intel c2q has 2 dual-core dies, the opteron I have seems to be two
    single cores and this magny thing has 2 many cores -- teh pun, sides
    aching :-)

    So the generalization to dies per socket seems sensible.





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