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    Subject[PATCH 4.9 053/119] cfq-iosched: fix the delay of cfq_groups vdisktime under iops mode
    Date
    4.9-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Hou Tao <houtao1@huawei.com>

    commit 5be6b75610cefd1e21b98a218211922c2feb6e08 upstream.

    When adding a cfq_group into the cfq service tree, we use CFQ_IDLE_DELAY
    as the delay of cfq_group's vdisktime if there have been other cfq_groups
    already.

    When cfq is under iops mode, commit 9a7f38c42c2b ("cfq-iosched: Convert
    from jiffies to nanoseconds") could result in a large iops delay and
    lead to an abnormal io schedule delay for the added cfq_group. To fix
    it, we just need to revert to the old CFQ_IDLE_DELAY value: HZ / 5
    when iops mode is enabled.

    Despite having the same value, the delay of a cfq_queue in idle class
    and the delay of cfq_group are different things, so I define two new
    macros for the delay of a cfq_group under time-slice mode and iops mode.

    Fixes: 9a7f38c42c2b ("cfq-iosched: Convert from jiffies to nanoseconds")
    Signed-off-by: Hou Tao <houtao1@huawei.com>
    Acked-by: Jan Kara <jack@suse.cz>
    Signed-off-by: Jens Axboe <axboe@fb.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    block/cfq-iosched.c | 17 +++++++++++++++--
    1 file changed, 15 insertions(+), 2 deletions(-)

    --- a/block/cfq-iosched.c
    +++ b/block/cfq-iosched.c
    @@ -36,9 +36,13 @@ static const u64 cfq_target_latency = (u
    static const int cfq_hist_divisor = 4;

    /*
    - * offset from end of service tree
    + * offset from end of queue service tree for idle class
    */
    #define CFQ_IDLE_DELAY (NSEC_PER_SEC / 5)
    +/* offset from end of group service tree under time slice mode */
    +#define CFQ_SLICE_MODE_GROUP_DELAY (NSEC_PER_SEC / 5)
    +/* offset from end of group service under IOPS mode */
    +#define CFQ_IOPS_MODE_GROUP_DELAY (HZ / 5)

    /*
    * below this threshold, we consider thinktime immediate
    @@ -1370,6 +1374,14 @@ cfq_group_service_tree_add(struct cfq_rb
    cfqg->vfraction = max_t(unsigned, vfr, 1);
    }

    +static inline u64 cfq_get_cfqg_vdisktime_delay(struct cfq_data *cfqd)
    +{
    + if (!iops_mode(cfqd))
    + return CFQ_SLICE_MODE_GROUP_DELAY;
    + else
    + return CFQ_IOPS_MODE_GROUP_DELAY;
    +}
    +
    static void
    cfq_group_notify_queue_add(struct cfq_data *cfqd, struct cfq_group *cfqg)
    {
    @@ -1389,7 +1401,8 @@ cfq_group_notify_queue_add(struct cfq_da
    n = rb_last(&st->rb);
    if (n) {
    __cfqg = rb_entry_cfqg(n);
    - cfqg->vdisktime = __cfqg->vdisktime + CFQ_IDLE_DELAY;
    + cfqg->vdisktime = __cfqg->vdisktime +
    + cfq_get_cfqg_vdisktime_delay(cfqd);
    } else
    cfqg->vdisktime = st->min_vdisktime;
    cfq_group_service_tree_add(st, cfqg);

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