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block: make queue flags non-atomic

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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>
This commit is contained in:
Nick Piggin
2008-04-29 14:48:33 +02:00
committed by Jens Axboe
parent 68154e90c9
commit 75ad23bc0f
13 changed files with 101 additions and 48 deletions
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29
drivers/scsi/scsi_lib.c
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@ -536,6 +536,9 @@ static void scsi_run_queue(struct request_queue *q)
!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 @@ static void scsi_run_queue(struct request_queue *q)
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 @@ struct request_queue *__scsi_alloc_queue(struct Scsi_Host *shost,
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