block: queue work on power efficient wq

Block layer uses workqueues for multiple purposes. There is no real dependency
of scheduling these on the cpu which scheduled them.

On a idle system, it is observed that and idle cpu wakes up many times just to
service this work. It would be better if we can schedule it on a cpu which the
scheduler believes to be the most appropriate one.

This patch replaces normal workqueues with power efficient versions.

Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Tejun Heo <tj@kernel.org>

1 files changed, 2 insertions, 1 deletions

diff --git a/block/blk-core.c b/block/blk-core.c
index 33c33bc99ddd..f0deb8bf89e1 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -3180,7 +3180,8 @@ int __init blk_dev_init(void)
 
         /* used for unplugging and affects IO latency/throughput - HIGHPRI */
         kblockd_workqueue = alloc_workqueue("kblockd",
-                                            WQ_MEM_RECLAIM | WQ_HIGHPRI, 0);
+                                            WQ_MEM_RECLAIM | WQ_HIGHPRI |
+                                            WQ_POWER_EFFICIENT, 0);
         if (!kblockd_workqueue)
                 panic("Failed to create kblockd\n");