blk: optimization for classic polling

This removes the dependency on interrupts to wake up task. Set task
state as TASK_RUNNING, if need_resched() returns true,
while polling for IO completion.
Earlier, polling task used to sleep, relying on interrupt to wake it up.
This made some IO take very long when interrupt-coalescing is enabled in
NVMe.

Reference:
http://lists.infradead.org/pipermail/linux-nvme/2018-February/015435.html

Changes since v2->v3:
	-using __set_current_state() instead of set_current_state()

Changes since v1->v2:
	-setting task state once in blk_poll, instead of multiple
callers.

Signed-off-by: Nitesh Shetty <[email protected]>
Signed-off-by: Jens Axboe <[email protected]>

diff --git a/block/blk-mq.c b/block/blk-mq.c
index df93102e21494dc7f98456e4376ce7c83fca56ab..357492712b0ea85362d2bbd6b2aa1687459cba66 100644 (file)
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -3164,6 +3164,7 @@ static bool __blk_mq_poll(struct blk_mq_hw_ctx *hctx, struct request *rq)
                cpu_relax();
        }
 
+       __set_current_state(TASK_RUNNING);
        return false;
 }