blkcg: don't use percpu for merged stats

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>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

2 files changed, 9 insertions, 23 deletions

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index 622fb4143226..6eedf3afa276 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 1de32fe0e2af..6c8e3e345426 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
 };