From: Ming Lei <ming.lei@redhat.com>
Date: Mon, 25 Jun 2018 19:31:48 +0800
Subject: [PATCH] blk-mq: remove synchronize_rcu() from
blk_mq_del_queue_tag_set()
Git-commit: 97889f9ac24f8d2fc8e703ea7f80c162bab10d4d
Patch-mainline: v4.19-rc1
References: bsc#1104967,FATE#325924
We have to remove synchronize_rcu() from blk_queue_cleanup(),
otherwise long delay can be caused during lun probe. For removing
it, we have to avoid to iterate the set->tag_list in IO path, eg,
blk_mq_sched_restart().
This patch reverts 5b79413946d (Revert "blk-mq: don't handle
TAG_SHARED in restart"). Given we have fixed enough IO hang issue,
and there isn't any reason to restart all queues in one tags any more,
see the following reasons:
1) blk-mq core can deal with shared-tags case well via blk_mq_get_driver_tag(),
which can wake up queues waiting for driver tag.
2) SCSI is a bit special because it may return BLK_STS_RESOURCE if queue,
target or host is ready, but SCSI built-in restart can cover all these well,
see scsi_end_request(), queue will be rerun after any request initiated from
this host/target is completed.
In my test on scsi_debug(8 luns), this patch may improve IOPS by 20% ~ 30%
when running I/O on these 8 luns concurrently.
Fixes: 705cda97ee3a ("blk-mq: Make it safe to use RCU to iterate over blk_mq_tag_set.tag_list")
Cc: Omar Sandoval <osandov@fb.com>
Cc: Bart Van Assche <bart.vanassche@wdc.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Martin K. Petersen <martin.petersen@oracle.com>
Cc: linux-scsi@vger.kernel.org
Reported-by: Andrew Jones <drjones@redhat.com>
Tested-by: Andrew Jones <drjones@redhat.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Acked-by: Hannes Reinecke <hare@suse.com>
---
block/blk-mq-sched.c | 85 +++-----------------------------------------------
block/blk-mq.c | 10 ++----
include/linux/blkdev.h | 2 --
3 files changed, 7 insertions(+), 90 deletions(-)
diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c
index 56c493c6cd90..4e027f6108ae 100644
--- a/block/blk-mq-sched.c
+++ b/block/blk-mq-sched.c
@@ -59,29 +59,16 @@ static void blk_mq_sched_mark_restart_hctx(struct blk_mq_hw_ctx *hctx)
if (test_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state))
return;
- if (hctx->flags & BLK_MQ_F_TAG_SHARED) {
- struct request_queue *q = hctx->queue;
-
- if (!test_and_set_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state))
- atomic_inc(&q->shared_hctx_restart);
- } else
- set_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state);
+ set_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state);
}
-static bool blk_mq_sched_restart_hctx(struct blk_mq_hw_ctx *hctx)
+void blk_mq_sched_restart(struct blk_mq_hw_ctx *hctx)
{
if (!test_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state))
- return false;
-
- if (hctx->flags & BLK_MQ_F_TAG_SHARED) {
- struct request_queue *q = hctx->queue;
-
- if (test_and_clear_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state))
- atomic_dec(&q->shared_hctx_restart);
- } else
- clear_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state);
+ return;
+ clear_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state);
- return blk_mq_run_hw_queue(hctx, true);
+ blk_mq_run_hw_queue(hctx, true);
}
/*
@@ -380,68 +367,6 @@ static bool blk_mq_sched_bypass_insert(struct blk_mq_hw_ctx *hctx,
return false;
}
-/**
- * list_for_each_entry_rcu_rr - iterate in a round-robin fashion over rcu list
- * @pos: loop cursor.
- * @skip: the list element that will not be examined. Iteration starts at
- * @skip->next.
- * @head: head of the list to examine. This list must have at least one
- * element, namely @skip.
- * @member: name of the list_head structure within typeof(*pos).
- */
-#define list_for_each_entry_rcu_rr(pos, skip, head, member) \
- for ((pos) = (skip); \
- (pos = (pos)->member.next != (head) ? list_entry_rcu( \
- (pos)->member.next, typeof(*pos), member) : \
- list_entry_rcu((pos)->member.next->next, typeof(*pos), member)), \
- (pos) != (skip); )
-
-/*
- * Called after a driver tag has been freed to check whether a hctx needs to
- * be restarted. Restarts @hctx if its tag set is not shared. Restarts hardware
- * queues in a round-robin fashion if the tag set of @hctx is shared with other
- * hardware queues.
- */
-void blk_mq_sched_restart(struct blk_mq_hw_ctx *const hctx)
-{
- struct blk_mq_tags *const tags = hctx->tags;
- struct blk_mq_tag_set *const set = hctx->queue->tag_set;
- struct request_queue *const queue = hctx->queue, *q;
- struct blk_mq_hw_ctx *hctx2;
- unsigned int i, j;
-
- if (set->flags & BLK_MQ_F_TAG_SHARED) {
- /*
- * If this is 0, then we know that no hardware queues
- * have RESTART marked. We're done.
- */
- if (!atomic_read(&queue->shared_hctx_restart))
- return;
-
- rcu_read_lock();
- list_for_each_entry_rcu_rr(q, queue, &set->tag_list,
- tag_set_list) {
- queue_for_each_hw_ctx(q, hctx2, i)
- if (hctx2->tags == tags &&
- blk_mq_sched_restart_hctx(hctx2))
- goto done;
- }
- j = hctx->queue_num + 1;
- for (i = 0; i < queue->nr_hw_queues; i++, j++) {
- if (j == queue->nr_hw_queues)
- j = 0;
- hctx2 = queue->queue_hw_ctx[j];
- if (hctx2->tags == tags &&
- blk_mq_sched_restart_hctx(hctx2))
- break;
- }
-done:
- rcu_read_unlock();
- } else {
- blk_mq_sched_restart_hctx(hctx);
- }
-}
-
void blk_mq_sched_insert_request(struct request *rq, bool at_head,
bool run_queue, bool async)
{
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -2335,15 +2335,10 @@ static void queue_set_hctx_shared(struct request_queue *q, bool shared)
int i;
queue_for_each_hw_ctx(q, hctx, i) {
- if (shared) {
- if (test_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state))
- atomic_inc(&q->shared_hctx_restart);
+ if (shared)
hctx->flags |= BLK_MQ_F_TAG_SHARED;
- } else {
- if (test_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state))
- atomic_dec(&q->shared_hctx_restart);
+ else
hctx->flags &= ~BLK_MQ_F_TAG_SHARED;
- }
}
}
@@ -2374,7 +2369,6 @@ static void blk_mq_del_queue_tag_set(struct request_queue *q)
blk_mq_update_tag_set_depth(set, false);
}
mutex_unlock(&set->tag_list_lock);
- synchronize_rcu();
INIT_LIST_HEAD(&q->tag_set_list);
}
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index ca5a8b046894..9d05646d5059 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -442,8 +442,6 @@ struct request_queue {
int nr_rqs[2]; /* # allocated [a]sync rqs */
int nr_rqs_elvpriv; /* # allocated rqs w/ elvpriv */
- atomic_t shared_hctx_restart;
-
struct blk_queue_stats *stats;
struct rq_wb *rq_wb;
--
2.16.4