Messages in this thread | | | Date | Wed, 09 Jul 2014 13:15:39 +0200 | From | Hannes Reinecke <> | Subject | Re: [PATCH 06/14] scsi: convert target_busy to an atomic_t |
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On 06/25/2014 06:51 PM, Christoph Hellwig wrote: > Avoid taking the host-wide host_lock to check the per-target queue limit. > Instead we do an atomic_inc_return early on to grab our slot in the queue, > and if nessecary decrement it after finishing all checks. > > Signed-off-by: Christoph Hellwig <hch@lst.de> > --- > drivers/scsi/scsi_lib.c | 52 ++++++++++++++++++++++++++------------------ > include/scsi/scsi_device.h | 4 ++-- > 2 files changed, 33 insertions(+), 23 deletions(-) > > diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c > index 18e6449..5e269d6 100644 > --- a/drivers/scsi/scsi_lib.c > +++ b/drivers/scsi/scsi_lib.c > @@ -294,7 +294,7 @@ void scsi_device_unbusy(struct scsi_device *sdev) > > spin_lock_irqsave(shost->host_lock, flags); > shost->host_busy--; > - starget->target_busy--; > + atomic_dec(&starget->target_busy); > if (unlikely(scsi_host_in_recovery(shost) && > (shost->host_failed || shost->host_eh_scheduled))) > scsi_eh_wakeup(shost); > @@ -361,7 +361,7 @@ static inline int scsi_device_is_busy(struct scsi_device *sdev) > static inline int scsi_target_is_busy(struct scsi_target *starget) > { > return ((starget->can_queue > 0 && > - starget->target_busy >= starget->can_queue) || > + atomic_read(&starget->target_busy) >= starget->can_queue) || > starget->target_blocked); > } > > @@ -1305,37 +1305,49 @@ 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; > + unsigned int busy; > > - spin_lock_irq(shost->host_lock); > if (starget->single_lun) { > + spin_lock_irq(shost->host_lock); > if (starget->starget_sdev_user && > - starget->starget_sdev_user != sdev) > - goto out; > + starget->starget_sdev_user != sdev) { > + spin_unlock_irq(shost->host_lock); > + return 0; > + } > starget->starget_sdev_user = sdev; > + spin_unlock_irq(shost->host_lock); > } > > - if (starget->target_busy == 0 && starget->target_blocked) { > + busy = atomic_inc_return(&starget->target_busy) - 1; > + if (busy == 0 && starget->target_blocked) { > /* > * unblock after target_blocked iterates to zero > */ > - if (--starget->target_blocked != 0) > - goto out; > + spin_lock_irq(shost->host_lock); > + if (--starget->target_blocked != 0) { > + spin_unlock_irq(shost->host_lock); > + goto out_dec; > + } > + spin_unlock_irq(shost->host_lock); > > 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); > - goto out; > - } > + if (starget->can_queue > 0 && busy >= starget->can_queue) > + goto starved; > + if (starget->target_blocked) > + goto starved; > > - scsi_target(sdev)->target_busy++; > - ret = 1; > -out: > + return 1; > + > +starved: > + spin_lock_irq(shost->host_lock); > + list_move_tail(&sdev->starved_entry, &shost->starved_list); > spin_unlock_irq(shost->host_lock); > - return ret; > +out_dec: > + atomic_dec(&starget->target_busy); > + return 0; > } > > /* > @@ -1445,7 +1457,7 @@ static void scsi_kill_request(struct request *req, struct request_queue *q) > spin_unlock(sdev->request_queue->queue_lock); > spin_lock(shost->host_lock); > shost->host_busy++; > - starget->target_busy++; > + atomic_inc(&starget->target_busy); > spin_unlock(shost->host_lock); > spin_lock(sdev->request_queue->queue_lock); > > @@ -1615,9 +1627,7 @@ static void scsi_request_fn(struct request_queue *q) > return; > > host_not_ready: > - spin_lock_irq(shost->host_lock); > - scsi_target(sdev)->target_busy--; > - spin_unlock_irq(shost->host_lock); > + atomic_dec(&scsi_target(sdev)->target_busy); > not_ready: > /* > * lock q, handle tag, requeue req, and decrement device_busy. We > diff --git a/include/scsi/scsi_device.h b/include/scsi/scsi_device.h > index 816e8a2..446f741 100644 > --- a/include/scsi/scsi_device.h > +++ b/include/scsi/scsi_device.h > @@ -290,8 +290,8 @@ struct scsi_target { > unsigned int expecting_lun_change:1; /* A device has reported > * a 3F/0E UA, other devices on > * the same target will also. */ > - /* commands actually active on LLD. protected by host lock. */ > - unsigned int target_busy; > + /* commands actually active on LLD. */ > + atomic_t target_busy; > /* > * LLDs should set this in the slave_alloc host template callout. > * If set to zero then there is not limit. > 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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