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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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