block: make queue flags non-atomic
We can save some atomic ops in the IO path, if we clearly define
the rules of how to modify the queue flags.
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index 67f412b..d545ad1 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -536,6 +536,9 @@
!shost->host_blocked && !shost->host_self_blocked &&
!((shost->can_queue > 0) &&
(shost->host_busy >= shost->can_queue))) {
+
+ int flagset;
+
/*
* As long as shost is accepting commands and we have
* starved queues, call blk_run_queue. scsi_request_fn
@@ -549,19 +552,20 @@
sdev = list_entry(shost->starved_list.next,
struct scsi_device, starved_entry);
list_del_init(&sdev->starved_entry);
- spin_unlock_irqrestore(shost->host_lock, flags);
+ spin_unlock(shost->host_lock);
+ spin_lock(sdev->request_queue->queue_lock);
+ flagset = test_bit(QUEUE_FLAG_REENTER, &q->queue_flags) &&
+ !test_bit(QUEUE_FLAG_REENTER,
+ &sdev->request_queue->queue_flags);
+ if (flagset)
+ queue_flag_set(QUEUE_FLAG_REENTER, sdev->request_queue);
+ __blk_run_queue(sdev->request_queue);
+ if (flagset)
+ queue_flag_clear(QUEUE_FLAG_REENTER, sdev->request_queue);
+ spin_unlock(sdev->request_queue->queue_lock);
- if (test_bit(QUEUE_FLAG_REENTER, &q->queue_flags) &&
- !test_and_set_bit(QUEUE_FLAG_REENTER,
- &sdev->request_queue->queue_flags)) {
- blk_run_queue(sdev->request_queue);
- clear_bit(QUEUE_FLAG_REENTER,
- &sdev->request_queue->queue_flags);
- } else
- blk_run_queue(sdev->request_queue);
-
- spin_lock_irqsave(shost->host_lock, flags);
+ spin_lock(shost->host_lock);
if (unlikely(!list_empty(&sdev->starved_entry)))
/*
* sdev lost a race, and was put back on the
@@ -1585,8 +1589,9 @@
blk_queue_max_segment_size(q, dma_get_max_seg_size(dev));
+ /* New queue, no concurrency on queue_flags */
if (!shost->use_clustering)
- clear_bit(QUEUE_FLAG_CLUSTER, &q->queue_flags);
+ queue_flag_clear_unlocked(QUEUE_FLAG_CLUSTER, q);
/*
* set a reasonable default alignment on word boundaries: the
