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    SubjectRe: [PATCH 23/24] cfq-iosched: collect stats from dead cfqgs
    Hey, Vivek.

    On Wed, Jan 02, 2013 at 11:24:15AM -0500, Vivek Goyal wrote:
    > On Fri, Dec 28, 2012 at 12:35:45PM -0800, Tejun Heo wrote:
    > > To support hierarchical stats, it's necessary to remember stats from
    > > dead children. Add cfqg->dead_stats and make a dying cfqg transfer
    > > its stats to the parent's dead-stats.
    >
    > Hi Tejun,
    >
    > Why not directly transfer stats to cfqg->stats. IOW, what's the advantage
    > of maintaining dead_stats separately.

    Backward compatibility? The existing stat cgroupfs files expect to
    see non-recursive stats.

    > > + cfqg_stats_merge(&parent->dead_stats, &cfqg->stats);
    > > + cfqg_stats_merge(&parent->dead_stats, &cfqg->dead_stats);
    > > + cfqg_stats_reset(&cfqg->stats);
    > > + cfqg_stats_reset(&cfqg->dead_stats);
    >
    > Anyway group will be marked offline and later freed. So resetting stats
    > might not be required.

    Yeah, it isn't strictly necessary. I tried to transfer the residual
    IOs between offline and release first so the resetting. Kinda like
    them there tho.

    > In fact if we have a realiable way of resetting status then online/offline
    > infrastructure might not be required? I think per cpu stats will be a
    > problem though and that's why we probably require logic to online/offline
    > the group?

    Hmmm? What do you mean?

    Thanks.

    --
    tejun


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