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    SubjectRe: [RFC] sched: CPU topology try
    On Wed, Dec 18, 2013 at 02:13:51PM +0100, Vincent Guittot wrote:
    > This patch applies on top of the two patches [1][2] that have been proposed by
    > Peter for creating a new way to initialize sched_domain. It includes some minor
    > compilation fixes and a trial of using this new method on ARM platform.
    > [1] https://lkml.org/lkml/2013/11/5/239
    > [2] https://lkml.org/lkml/2013/11/5/449
    >
    > Based on the results of this tests, my feeling about this new way to init the
    > sched_domain is a bit mitigated.

    Yay :-)

    > We can add more levels that will describe other dependency/independency like
    > the frequency scaling dependency and as a result the final sched_domain
    > topology will have additional levels (if they have not been removed during
    > the degenerate sequence)

    Yeah, this 'creative' use of degenerate domains is pretty neat ;-)

    > My concern is about the configuration of the table that is used to create the
    > sched_domain. Some levels are "duplicated" with different flags configuration
    > which make the table not easily readable and we must also take care of the
    > order because parents have to gather all cpus of its childs. So we must
    > choose which capabilities will be a subset of the other one. The order is
    > almost straight forward when we describe 1 or 2 kind of capabilities
    > (package ressource sharing and power sharing) but it can become complex if we
    > want to add more.

    I think I see what you're saying, although I hope that won't actually
    happen in real hardware -- that said, people do tend to do crazy with
    these ARM chips :/

    We should also try and be conservative in the topology flags we want to
    add, which should further reduce the amount of pain here.

    For now I do think this is a viable approach.. Yes its a bit cumbersome
    for these asymmetric systems but it does give us enough to start
    playing.

    I yet have to read Morton's emails on the P and C states, will try to
    have a look at those tomorrow with a hopefully fresher brain -- somehow
    its the end of the day already..


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