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    SubjectRe: [PATCH] schedstats additions
    Rick Lindsley wrote:
    > I have a patch here to provide more useful statistics for me. Basically
    > it moves a lot more of the balancing information into the domains instead
    > of the runqueue, where it is nearly useless on multi-domain setups (eg.
    > SMT+SMP, SMP+NUMA).
    >
    > It requires a version number bump, but that isn't much of an issue because
    > I think we're about the only two using it at the moment. But your tools
    > will need a little bit of work.
    >
    > What do you think?
    >
    > The idea of moving some counters from runqueues to domains is fine in
    > general, but I've some questions about a couple of specific changes in
    > your patch.
    >
    > It looks to me like there are some changes in try_to_wake_up() that
    > aren't schedstats related, although schedstats code is among some
    > that is moved around. Is there some code there that should be
    > broken out separately?
    >

    There is, yes. I'll be sure to seperate it.

    > alb_cnt
    > by moving this, we won't get an accurate look at the number of
    > times we called active_load_balance and returned immediately
    > because nr_running had slipped to 0 or 1. how about we add
    > another counter to count that too, and/or change the name of
    > this one?
    >

    OK.

    > lb_balanced
    > are you sure lb_balanced[idle] can't be deduced from lb_cnt[idle]
    > and lb_failed[idle]?
    >

    I don't think so, because you also have the success case, which is
    !balanced && !failed.

    > ttwu_attempts
    > ttwu_moved
    > removing these makes it harder to determine how successful
    > try_to_wake_up() was at moving a process. What counters would
    > I use to get this information if these were removed?
    >

    ttwu_cnt in the rq stats, and ttwu_wake_affine / ttwu_wake_balance
    in the domain stats.

    > ttwu_remote
    > ttwu_wake_remote
    > so what's the one line description of what these count now?
    >

    ttwu_remote/ttwu_wake_remote are the number of times a runqueue has
    woken a remote task / a remote task within that domain, respectively.
    Regardless of whether or not it gets pulled onto the local CPU.

    > smt_cnt
    > sbe_cnt
    > how might I see how often sched_migrate_task() and sched_exec()
    > were called if these were deleted?
    >

    sbe_pushed should basically be the same as smt_cnt, barring rare
    races with the cpus_allowed mask. I guess sbe_cnt doesn't have to
    go.

    > lb_pulled
    > Rather than add another counter here, would it be as effective
    > to make pt_gained a domain counter? Looks like you're collecting

    Yeah removing the runqueue counters for these would be good.

    > the same information. pt_lost would have to remain a runqueue
    > counter, though, since losing a task has nothing to do with a
    > particular domain.


    Whatever domain that the pulling CPU was in, is also a fair candidate
    for pt_lost. Remember, all the domains are per-CPU so any information
    you can get from a per-runqueue counter you can also get from a domain
    counter.

    I'll make a few changes and give you another look. Thanks for the comments.
    -
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