Messages in this thread | | | Date | Wed, 09 Jul 2014 13:14:35 +0200 | From | Hannes Reinecke <> | Subject | Re: [PATCH 05/14] scsi: push host_lock down into scsi_{host,target}_queue_ready |
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On 06/25/2014 06:51 PM, Christoph Hellwig wrote: > 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> > --- > drivers/scsi/scsi_lib.c | 75 ++++++++++++++++++++++++----------------------- > 1 file changed, 39 insertions(+), 36 deletions(-) > > diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c > index 6989b6f..18e6449 100644 > --- a/drivers/scsi/scsi_lib.c > +++ b/drivers/scsi/scsi_lib.c > @@ -1300,18 +1300,18 @@ static inline int scsi_dev_queue_ready(struct request_queue *q, > /* > * scsi_target_queue_ready: checks if there we can send commands to target > * @sdev: scsi device on starget to check. > - * > - * Called with the host lock held. > */ > static inline int scsi_target_queue_ready(struct Scsi_Host *shost, > struct scsi_device *sdev) > { > struct scsi_target *starget = scsi_target(sdev); > + int ret = 0; > > + spin_lock_irq(shost->host_lock); > if (starget->single_lun) { > if (starget->starget_sdev_user && > starget->starget_sdev_user != sdev) > - return 0; > + goto out; > starget->starget_sdev_user = sdev; > } > > @@ -1319,57 +1319,66 @@ static inline int scsi_target_queue_ready(struct Scsi_Host *shost, > /* > * unblock after target_blocked iterates to zero > */ > - if (--starget->target_blocked == 0) { > - SCSI_LOG_MLQUEUE(3, starget_printk(KERN_INFO, starget, > - "unblocking target at zero depth\n")); > - } else > - return 0; > + if (--starget->target_blocked != 0) > + goto out; > + > + SCSI_LOG_MLQUEUE(3, starget_printk(KERN_INFO, starget, > + "unblocking target at zero depth\n")); > } > > if (scsi_target_is_busy(starget)) { > list_move_tail(&sdev->starved_entry, &shost->starved_list); > - return 0; > + goto out; > } > > - return 1; > + scsi_target(sdev)->target_busy++; > + ret = 1; > +out: > + spin_unlock_irq(shost->host_lock); > + return ret; > } > > /* > * scsi_host_queue_ready: if we can send requests to shost, return 1 else > * return 0. We must end up running the queue again whenever 0 is > * returned, else IO can hang. > - * > - * Called with host_lock held. > */ > static inline int scsi_host_queue_ready(struct request_queue *q, > struct Scsi_Host *shost, > struct scsi_device *sdev) > { > + int ret = 0; > + > + spin_lock_irq(shost->host_lock); > + > if (scsi_host_in_recovery(shost)) > - return 0; > + goto out; > if (shost->host_busy == 0 && shost->host_blocked) { > /* > * unblock after host_blocked iterates to zero > */ > - if (--shost->host_blocked == 0) { > - SCSI_LOG_MLQUEUE(3, > - shost_printk(KERN_INFO, shost, > - "unblocking host at zero depth\n")); > - } else { > - return 0; > - } > + if (--shost->host_blocked != 0) > + goto out; > + > + SCSI_LOG_MLQUEUE(3, > + shost_printk(KERN_INFO, shost, > + "unblocking host at zero depth\n")); > } > if (scsi_host_is_busy(shost)) { > if (list_empty(&sdev->starved_entry)) > list_add_tail(&sdev->starved_entry, &shost->starved_list); > - return 0; > + goto out; > } > > /* We're OK to process the command, so we can't be starved */ > if (!list_empty(&sdev->starved_entry)) > list_del_init(&sdev->starved_entry); > > - return 1; > + shost->host_busy++; > + ret = 1; > +out: > + spin_unlock_irq(shost->host_lock); > + return ret; > } > > /* > @@ -1550,7 +1559,7 @@ static void scsi_request_fn(struct request_queue *q) > blk_start_request(req); > sdev->device_busy++; > > - spin_unlock(q->queue_lock); > + spin_unlock_irq(q->queue_lock); > cmd = req->special; > if (unlikely(cmd == NULL)) { > printk(KERN_CRIT "impossible request in %s.\n" > @@ -1560,7 +1569,6 @@ static void scsi_request_fn(struct request_queue *q) > blk_dump_rq_flags(req, "foo"); > BUG(); > } > - spin_lock(shost->host_lock); > > /* > * We hit this when the driver is using a host wide > @@ -1571,9 +1579,11 @@ static void scsi_request_fn(struct request_queue *q) > * a run when a tag is freed. > */ > if (blk_queue_tagged(q) && !blk_rq_tagged(req)) { > + spin_lock_irq(shost->host_lock); > if (list_empty(&sdev->starved_entry)) > list_add_tail(&sdev->starved_entry, > &shost->starved_list); > + spin_unlock_irq(shost->host_lock); > goto not_ready; > } > > @@ -1581,16 +1591,7 @@ static void scsi_request_fn(struct request_queue *q) > goto not_ready; > > if (!scsi_host_queue_ready(q, shost, sdev)) > - goto not_ready; > - > - scsi_target(sdev)->target_busy++; > - shost->host_busy++; > - > - /* > - * XXX(hch): This is rather suboptimal, scsi_dispatch_cmd will > - * take the lock again. > - */ > - spin_unlock_irq(shost->host_lock); > + goto host_not_ready; > > /* > * Finally, initialize any error handling parameters, and set up > @@ -1613,9 +1614,11 @@ static void scsi_request_fn(struct request_queue *q) > > return; > > - not_ready: > + host_not_ready: > + spin_lock_irq(shost->host_lock); > + scsi_target(sdev)->target_busy--; > spin_unlock_irq(shost->host_lock); > - > + not_ready: > /* > * lock q, handle tag, requeue req, and decrement device_busy. We > * must return with queue_lock held. > Reviewed-by: Hannes Reinecke <hare@suse.de>
Cheers,
Hannes -- Dr. Hannes Reinecke zSeries & Storage hare@suse.de +49 911 74053 688 SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg GF: J. Hawn, J. Guild, F. Imendörffer, HRB 16746 (AG Nürnberg) -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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