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    Subject[PATCH] block: Improve think time sampling for CFQ
    Date
    Avoid taking a think time sample when the cfqq is not a sync queue or not
    currently active or till its first request in the ongoing timeslice
    completes.

    Signed-off by: Divyesh Shah <dpshah@google.com>
    ---
    This applies to Linus's kernel tree.

    block/cfq-iosched.c | 15 +++++++++++----
    1 files changed, 11 insertions(+), 4 deletions(-)
    diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
    index fd7080e..1657d4f 100644
    --- a/block/cfq-iosched.c
    +++ b/block/cfq-iosched.c
    @@ -1904,10 +1904,17 @@ err:
    }

    static void
    -cfq_update_io_thinktime(struct cfq_data *cfqd, struct cfq_io_context *cic)
    +cfq_update_io_thinktime(struct cfq_data *cfqd, struct cfq_queue *cfqq,
    + struct cfq_io_context *cic)
    {
    - unsigned long elapsed = jiffies - cic->last_end_request;
    - unsigned long ttime = min(elapsed, 2UL * cfqd->cfq_slice_idle);
    + unsigned long elapsed, ttime;
    +
    + if (!cfq_cfqq_sync(cfqq) || cfqq != cfqd->active_queue ||
    + cfq_cfqq_slice_new(cfqq))
    + return;
    +
    + elapsed = jiffies - cic->last_end_request;
    + ttime = min(elapsed, 2UL * cfqd->cfq_slice_idle);

    cic->ttime_samples = (7*cic->ttime_samples + 256) / 8;
    cic->ttime_total = (7*cic->ttime_total + 256*ttime) / 8;
    @@ -2072,7 +2079,7 @@ cfq_rq_enqueued(struct cfq_data *cfqd, struct cfq_queue *cfqq,
    if (rq_is_meta(rq))
    cfqq->meta_pending++;

    - cfq_update_io_thinktime(cfqd, cic);
    + cfq_update_io_thinktime(cfqd, cfqq, cic);
    cfq_update_io_seektime(cfqd, cic, rq);
    cfq_update_idle_window(cfqd, cfqq, cic);



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