cfq-iosched: Make IO merge related stats per cpu

Make BLKIO_STAT_MERGED per cpu hence gettring rid of need of taking
blkg->stats_lock.

Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>

2 files changed, 19 insertions, 7 deletions

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index e41cc6f2ccc..07371cfdfae 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -441,15 +441,27 @@ void blkiocg_update_completion_stats(struct blkio_group *blkg,
 }
 EXPORT_SYMBOL_GPL(blkiocg_update_completion_stats);
 
+/*  Merged stats are per cpu.  */
 void blkiocg_update_io_merged_stats(struct blkio_group *blkg, bool direction,
                                         bool sync)
 {
+        struct blkio_group_stats_cpu *stats_cpu;
         unsigned long flags;
 
-        spin_lock_irqsave(&blkg->stats_lock, flags);
-        blkio_add_stat(blkg->stats.stat_arr[BLKIO_STAT_MERGED], 1, direction,
-                        sync);
-        spin_unlock_irqrestore(&blkg->stats_lock, flags);
+        /*
+         * 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(blkg->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);
 }
 EXPORT_SYMBOL_GPL(blkiocg_update_io_merged_stats);
 
@@ -1244,7 +1256,7 @@ 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_MERGED, 1, 0);
+                                                BLKIO_STAT_CPU_MERGED, 1, 1);
                 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 26222679809..a71d2904ffb 100644
--- a/block/blk-cgroup.h
+++ b/block/blk-cgroup.h
@@ -39,8 +39,6 @@ enum stat_type {
         BLKIO_STAT_SERVICE_TIME = 0,
         /* Total time spent waiting in scheduler queue in ns */
         BLKIO_STAT_WAIT_TIME,
-        /* Number of IOs merged */
-        BLKIO_STAT_MERGED,
         /* Number of IOs queued up */
         BLKIO_STAT_QUEUED,
         /* All the single valued stats go below this */
@@ -63,6 +61,8 @@ 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
 };