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scsi: push host_lock down into scsi_{host,target}_queue_ready
Prepare for not taking a host-wide lock in the dispatch path by pushing the lock down into the places that actually need it. Note that this patch is just a preparation step, as it will actually increase lock roundtrips and thus decrease performance on its own. Signed-off-by: Christoph Hellwig <hch@lst.de> Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com> Reviewed-by: Hannes Reinecke <hare@suse.de> Reviewed-by: Webb Scales <webbnh@hp.com> Acked-by: Jens Axboe <axboe@kernel.dk> Tested-by: Bart Van Assche <bvanassche@acm.org> Tested-by: Robert Elliott <elliott@hp.com>
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3b5382c459
commit
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1 changed files with 39 additions and 36 deletions
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@ -1274,18 +1274,18 @@ static inline int scsi_dev_queue_ready(struct request_queue *q,
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/*
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* scsi_target_queue_ready: checks if there we can send commands to target
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* @sdev: scsi device on starget to check.
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*
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* Called with the host lock held.
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*/
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static inline int scsi_target_queue_ready(struct Scsi_Host *shost,
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struct scsi_device *sdev)
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{
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struct scsi_target *starget = scsi_target(sdev);
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int ret = 0;
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spin_lock_irq(shost->host_lock);
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if (starget->single_lun) {
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if (starget->starget_sdev_user &&
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starget->starget_sdev_user != sdev)
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return 0;
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goto out;
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starget->starget_sdev_user = sdev;
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}
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@ -1293,57 +1293,66 @@ static inline int scsi_target_queue_ready(struct Scsi_Host *shost,
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/*
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* unblock after target_blocked iterates to zero
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*/
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if (--starget->target_blocked == 0) {
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SCSI_LOG_MLQUEUE(3, starget_printk(KERN_INFO, starget,
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"unblocking target at zero depth\n"));
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} else
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return 0;
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if (--starget->target_blocked != 0)
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goto out;
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SCSI_LOG_MLQUEUE(3, starget_printk(KERN_INFO, starget,
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"unblocking target at zero depth\n"));
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}
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if (scsi_target_is_busy(starget)) {
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list_move_tail(&sdev->starved_entry, &shost->starved_list);
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return 0;
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goto out;
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}
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return 1;
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scsi_target(sdev)->target_busy++;
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ret = 1;
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out:
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spin_unlock_irq(shost->host_lock);
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return ret;
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}
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/*
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* scsi_host_queue_ready: if we can send requests to shost, return 1 else
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* return 0. We must end up running the queue again whenever 0 is
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* returned, else IO can hang.
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*
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* Called with host_lock held.
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*/
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static inline int scsi_host_queue_ready(struct request_queue *q,
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struct Scsi_Host *shost,
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struct scsi_device *sdev)
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{
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int ret = 0;
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spin_lock_irq(shost->host_lock);
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if (scsi_host_in_recovery(shost))
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return 0;
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goto out;
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if (shost->host_busy == 0 && shost->host_blocked) {
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/*
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* unblock after host_blocked iterates to zero
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*/
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if (--shost->host_blocked == 0) {
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SCSI_LOG_MLQUEUE(3,
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shost_printk(KERN_INFO, shost,
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"unblocking host at zero depth\n"));
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} else {
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return 0;
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}
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if (--shost->host_blocked != 0)
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goto out;
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SCSI_LOG_MLQUEUE(3,
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shost_printk(KERN_INFO, shost,
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"unblocking host at zero depth\n"));
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}
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if (scsi_host_is_busy(shost)) {
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if (list_empty(&sdev->starved_entry))
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list_add_tail(&sdev->starved_entry, &shost->starved_list);
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return 0;
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goto out;
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}
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/* We're OK to process the command, so we can't be starved */
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if (!list_empty(&sdev->starved_entry))
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list_del_init(&sdev->starved_entry);
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return 1;
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shost->host_busy++;
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ret = 1;
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out:
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spin_unlock_irq(shost->host_lock);
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return ret;
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}
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/*
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@ -1524,7 +1533,7 @@ static void scsi_request_fn(struct request_queue *q)
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blk_start_request(req);
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sdev->device_busy++;
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spin_unlock(q->queue_lock);
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spin_unlock_irq(q->queue_lock);
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cmd = req->special;
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if (unlikely(cmd == NULL)) {
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printk(KERN_CRIT "impossible request in %s.\n"
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@ -1534,7 +1543,6 @@ static void scsi_request_fn(struct request_queue *q)
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blk_dump_rq_flags(req, "foo");
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BUG();
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}
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spin_lock(shost->host_lock);
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/*
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* We hit this when the driver is using a host wide
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@ -1545,9 +1553,11 @@ static void scsi_request_fn(struct request_queue *q)
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* a run when a tag is freed.
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*/
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if (blk_queue_tagged(q) && !blk_rq_tagged(req)) {
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spin_lock_irq(shost->host_lock);
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if (list_empty(&sdev->starved_entry))
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list_add_tail(&sdev->starved_entry,
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&shost->starved_list);
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spin_unlock_irq(shost->host_lock);
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goto not_ready;
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}
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@ -1555,16 +1565,7 @@ static void scsi_request_fn(struct request_queue *q)
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goto not_ready;
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if (!scsi_host_queue_ready(q, shost, sdev))
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goto not_ready;
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scsi_target(sdev)->target_busy++;
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shost->host_busy++;
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/*
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* XXX(hch): This is rather suboptimal, scsi_dispatch_cmd will
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* take the lock again.
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*/
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spin_unlock_irq(shost->host_lock);
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goto host_not_ready;
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/*
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* Finally, initialize any error handling parameters, and set up
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@ -1587,9 +1588,11 @@ static void scsi_request_fn(struct request_queue *q)
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return;
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not_ready:
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host_not_ready:
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spin_lock_irq(shost->host_lock);
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scsi_target(sdev)->target_busy--;
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spin_unlock_irq(shost->host_lock);
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not_ready:
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/*
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* lock q, handle tag, requeue req, and decrement device_busy. We
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* must return with queue_lock held.
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