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Commit 476f8c98 authored by Ming Lei's avatar Ming Lei Committed by Jens Axboe
Browse files

blk-mq: avoid to write intermediate result to hctx->next_cpu 



This patch figures out the final selected CPU, then writes
it to hctx->next_cpu once, then we can avoid to intermediate
next cpu observed from other dispatch paths.

Cc: Stefan Haberland <sth@linux.vnet.ibm.com>
Tested-by: default avatarChristian Borntraeger <borntraeger@de.ibm.com>
Reviewed-by: default avatarChristoph Hellwig <hch@lst.de>
Reviewed-by: default avatarSagi Grimberg <sagi@grimberg.me>
Signed-off-by: default avatarMing Lei <ming.lei@redhat.com>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent bffa9909

block/blk-mq.c

+9 −8
Original line number Diff line number Diff line
@@ -1344,14 +1344,14 @@ static void __blk_mq_run_hw_queue(struct blk_mq_hw_ctx *hctx) 
static int blk_mq_hctx_next_cpu(struct blk_mq_hw_ctx *hctx)

{

	bool tried = false;

	int next_cpu = hctx->next_cpu;



	if (hctx->queue->nr_hw_queues == 1)

		return WORK_CPU_UNBOUND;



	if (--hctx->next_cpu_batch <= 0) {

		int next_cpu;

select_cpu:

		next_cpu = cpumask_next_and(hctx->next_cpu, hctx->cpumask,

		next_cpu = cpumask_next_and(next_cpu, hctx->cpumask,

				cpu_online_mask);

		if (next_cpu >= nr_cpu_ids)

			next_cpu = cpumask_first_and(hctx->cpumask, cpu_online_mask);
@@ -1361,9 +1361,7 @@ static int blk_mq_hctx_next_cpu(struct blk_mq_hw_ctx *hctx) 
		 * is set correctly for not breaking workqueue.

		 */

		if (next_cpu >= nr_cpu_ids)

			hctx->next_cpu = cpumask_first(hctx->cpumask);

		else

			hctx->next_cpu = next_cpu;

			next_cpu = cpumask_first(hctx->cpumask);

		hctx->next_cpu_batch = BLK_MQ_CPU_WORK_BATCH;

	}
@@ -1371,7 +1369,7 @@ static int blk_mq_hctx_next_cpu(struct blk_mq_hw_ctx *hctx) 
	 * Do unbound schedule if we can't find a online CPU for this hctx,

	 * and it should only happen in the path of handling CPU DEAD.

	 */

	if (!cpu_online(hctx->next_cpu)) {

	if (!cpu_online(next_cpu)) {

		if (!tried) {

			tried = true;

			goto select_cpu;
@@ -1381,10 +1379,13 @@ static int blk_mq_hctx_next_cpu(struct blk_mq_hw_ctx *hctx) 
		 * Make sure to re-select CPU next time once after CPUs

		 * in hctx->cpumask become online again.

		 */

		hctx->next_cpu = next_cpu;

		hctx->next_cpu_batch = 1;

		return WORK_CPU_UNBOUND;

	}

	return hctx->next_cpu;



	hctx->next_cpu = next_cpu;

	return next_cpu;

}



static void __blk_mq_delay_run_hw_queue(struct blk_mq_hw_ctx *hctx, bool async,