[v2,RESENT] blk: optimization for classic polling
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Message ID 1518548206-4766-1-git-send-email-nj.shetty@samsung.com
State New
Headers show

Commit Message

Nitesh Shetty Feb. 13, 2018, 6:56 p.m. UTC
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 v1:
	-setting task state once in blk_poll, instead of multiple
callers.
Signed-off-by: Nitesh Shetty <nj.shetty@samsung.com>
---
 block/blk-mq.c | 1 +
 1 file changed, 1 insertion(+)

Comments

Jens Axboe Feb. 13, 2018, 2:42 p.m. UTC | #1
On 2/13/18 11:56 AM, Nitesh Shetty wrote:
> 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.

__set_current_state() should suffice here.

Patch
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diff --git a/block/blk-mq.c b/block/blk-mq.c
index df93102..40285fe 100644
--- 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;
 }