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    SubjectRe: [patch] sched: schedstat needs a diet
    On Wed, 2007-10-17 at 09:23 +0200, Ingo Molnar wrote:
    > * Ken Chen <> wrote:
    > > schedstat is useful in investigating CPU scheduler behavior. Ideally,
    > > I think it is beneficial to have it on all the time. However, the
    > > cost of turning it on in production system is quite high, largely due
    > > to number of events it collects and also due to its large memory
    > > footprint.
    > >
    > > Most of the fields probably don't need to be full 64-bit on 64-bit
    > > arch. Rolling over 4 billion events will most like take a long time
    > > and user space tool can be made to accommodate that. I'm proposing
    > > kernel to cut back most of variable width on 64-bit system. (note,
    > > the following patch doesn't affect 32-bit system).
    > thanks, applied.
    > note that current -git has a whole bunch of new schedstats fields in
    > /proc/<PID>/sched which can be used to track the exact balancing
    > behavior of tasks. It can be cleared via echoing 0 to the file - so
    > overflow is not an issue. Most of those new fields should probably be
    > unsigned int too. (they are u64 right now.)

    FWIW I can't see how this patch saves a _lot_ of space. The stats are
    per domain or per rq, neither are things that have a lot of instances.

    That said, I have no actual objection to the patch, just not getting it.

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