From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: From: Ming Lei To: Jens Axboe Cc: linux-block@vger.kernel.org, Ming Lei , Andrew Jones , linux-scsi@vger.kernel.org, "Martin K. Petersen" , Christoph Hellwig Subject: [PATCH V2] blk-mq: avoid to synchronize rcu inside blk_cleanup_queue() Date: Sat, 23 Jun 2018 06:12:19 +0800 Message-Id: <20180622221219.6469-1-ming.lei@redhat.com> List-ID: SCSI probing may synchronously create and destroy a lot of request_queues for non-existent devices. Any synchronize_rcu() in queue creation or destroy path may introduce long latency during booting, see detailed description in comment of blk_register_queue(). This patch removes two synchronize_rcu() inside blk_cleanup_queue() for this case: 1) commit c2856ae2f315d75(blk-mq: quiesce queue before freeing queue) need synchronize_rcu() for implementing blk_mq_quiesce_queue(), but when queue isn't initialized, it isn't necessary to do that since only pass-through requests are involved, no original issue in scsi_execute() at all. 2) when only one request queue is attached to tags, no necessary to call synchronize_rcu() too. Without this patch, it may take more 20+ seconds for virtio-scsi to complete disk probe. With this patch, the time becomes less than 100ms. Reported-by: Andrew Jones Cc: Andrew Jones Cc: linux-scsi@vger.kernel.org Cc: "Martin K. Petersen" Cc: Christoph Hellwig Signed-off-by: Ming Lei --- block/blk-core.c | 8 ++++++-- block/blk-mq.c | 5 ++++- 2 files changed, 10 insertions(+), 3 deletions(-) diff --git a/block/blk-core.c b/block/blk-core.c index cf0ee764b908..f0129e20b773 100644 --- a/block/blk-core.c +++ b/block/blk-core.c @@ -766,9 +766,13 @@ void blk_cleanup_queue(struct request_queue *q) * make sure all in-progress dispatch are completed because * blk_freeze_queue() can only complete all requests, and * dispatch may still be in-progress since we dispatch requests - * from more than one contexts + * from more than one contexts. + * + * No need to quiesce queue if it isn't initialized yet since + * blk_freeze_queue() should be enough for cases of passthrough + * request. */ - if (q->mq_ops) + if (q->mq_ops && blk_queue_init_done(q)) blk_mq_quiesce_queue(q); /* for synchronous bio-based driver finish in-flight integrity i/o */ diff --git a/block/blk-mq.c b/block/blk-mq.c index 70c65bb6c013..8a6771ac0adb 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -2351,6 +2351,7 @@ static void blk_mq_update_tag_set_depth(struct blk_mq_tag_set *set, static void blk_mq_del_queue_tag_set(struct request_queue *q) { struct blk_mq_tag_set *set = q->tag_set; + bool shared; mutex_lock(&set->tag_list_lock); list_del_rcu(&q->tag_set_list); @@ -2360,8 +2361,10 @@ static void blk_mq_del_queue_tag_set(struct request_queue *q) /* update existing queue */ blk_mq_update_tag_set_depth(set, false); } + shared = set->flags & BLK_MQ_F_TAG_SHARED; mutex_unlock(&set->tag_list_lock); - synchronize_rcu(); + if (shared) + synchronize_rcu(); INIT_LIST_HEAD(&q->tag_set_list); } -- 2.9.5