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    Subject[PATCH 2/5] blkcg: don't use percpu for merged stats
    Date
    With recent plug merge updates, merged stats are no longer called for
    plug merges and now only updated while holding queue_lock. As
    stats_lock is scheduled to be removed, there's no reason to use percpu
    for merged stats. Don't use percpu for merged stats.

    Signed-off-by: Tejun Heo <tj@kernel.org>
    Cc: Vivek Goyal <vgoyal@redhat.com>
    ---
    block/blk-cgroup.c | 26 ++++++--------------------
    block/blk-cgroup.h | 6 +++---
    2 files changed, 9 insertions(+), 23 deletions(-)

    diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
    index 622fb41..6eedf3a 100644
    --- a/block/blk-cgroup.c
    +++ b/block/blk-cgroup.c
    @@ -451,27 +451,13 @@ void blkiocg_update_io_merged_stats(struct blkio_group *blkg,
    bool direction, bool sync)
    {
    struct blkg_policy_data *pd = blkg->pd[pol->plid];
    - struct blkio_group_stats_cpu *stats_cpu;
    + struct blkio_group_stats *stats;
    unsigned long flags;

    - /* If per cpu stats are not allocated yet, don't do any accounting. */
    - if (pd->stats_cpu == NULL)
    - return;
    -
    - /*
    - * Disabling interrupts to provide mutual exclusion between two
    - * writes on same cpu. It probably is not needed for 64bit. Not
    - * optimizing that case yet.
    - */
    - local_irq_save(flags);
    -
    - stats_cpu = this_cpu_ptr(pd->stats_cpu);
    -
    - u64_stats_update_begin(&stats_cpu->syncp);
    - blkio_add_stat(stats_cpu->stat_arr_cpu[BLKIO_STAT_CPU_MERGED], 1,
    - direction, sync);
    - u64_stats_update_end(&stats_cpu->syncp);
    - local_irq_restore(flags);
    + spin_lock_irqsave(&blkg->stats_lock, flags);
    + stats = &pd->stats;
    + blkio_add_stat(stats->stat_arr[BLKIO_STAT_MERGED], 1, direction, sync);
    + spin_unlock_irqrestore(&blkg->stats_lock, flags);
    }
    EXPORT_SYMBOL_GPL(blkiocg_update_io_merged_stats);

    @@ -1342,7 +1328,7 @@ static int blkiocg_file_read_map(struct cgroup *cgrp, struct cftype *cft,
    BLKIO_STAT_WAIT_TIME, 1, 0);
    case BLKIO_PROP_io_merged:
    return blkio_read_blkg_stats(blkcg, cft, cb,
    - BLKIO_STAT_CPU_MERGED, 1, 1);
    + BLKIO_STAT_MERGED, 1, 0);
    case BLKIO_PROP_io_queued:
    return blkio_read_blkg_stats(blkcg, cft, cb,
    BLKIO_STAT_QUEUED, 1, 0);
    diff --git a/block/blk-cgroup.h b/block/blk-cgroup.h
    index 1de32fe..6c8e3e3 100644
    --- a/block/blk-cgroup.h
    +++ b/block/blk-cgroup.h
    @@ -29,10 +29,12 @@ enum blkio_policy_id {
    #ifdef CONFIG_BLK_CGROUP

    enum stat_type {
    + /* Number of IOs merged */
    + BLKIO_STAT_MERGED,
    /* Total time spent (in ns) between request dispatch to the driver and
    * request completion for IOs doen by this cgroup. This may not be
    * accurate when NCQ is turned on. */
    - BLKIO_STAT_SERVICE_TIME = 0,
    + BLKIO_STAT_SERVICE_TIME,
    /* Total time spent waiting in scheduler queue in ns */
    BLKIO_STAT_WAIT_TIME,
    /* Number of IOs queued up */
    @@ -57,8 +59,6 @@ enum stat_type_cpu {
    BLKIO_STAT_CPU_SERVICE_BYTES,
    /* Total IOs serviced, post merge */
    BLKIO_STAT_CPU_SERVICED,
    - /* Number of IOs merged */
    - BLKIO_STAT_CPU_MERGED,
    BLKIO_STAT_CPU_NR
    };

    --
    1.7.7.3


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