From mboxrd@z Thu Jan 1 00:00:00 1970 From: Hannes Reinecke Subject: Re: [PATCH 10/14] scsi: only maintain target_blocked if the driver has a target queue limit Date: Wed, 09 Jul 2014 13:19:41 +0200 Message-ID: <53BD254D.4000806@suse.de> References: <1403715121-1201-1-git-send-email-hch@lst.de> <1403715121-1201-11-git-send-email-hch@lst.de> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: <1403715121-1201-11-git-send-email-hch@lst.de> Sender: linux-kernel-owner@vger.kernel.org To: Christoph Hellwig , James Bottomley Cc: Jens Axboe , Bart Van Assche , Robert Elliott , linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org List-Id: linux-scsi@vger.kernel.org On 06/25/2014 06:51 PM, Christoph Hellwig wrote: > This saves us an atomic operation for each I/O submission and complet= ion > for the usual case where the driver doesn't set a per-target can_queu= e > value. Only a few iscsi hardware offload drivers set the per-target > can_queue value at the moment. > > Signed-off-by: Christoph Hellwig > --- > drivers/scsi/scsi_lib.c | 17 ++++++++++++----- > 1 file changed, 12 insertions(+), 5 deletions(-) > > diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c > index a39d5ba..a64b9d3 100644 > --- a/drivers/scsi/scsi_lib.c > +++ b/drivers/scsi/scsi_lib.c > @@ -295,7 +295,8 @@ void scsi_device_unbusy(struct scsi_device *sdev) > unsigned long flags; > > atomic_dec(&shost->host_busy); > - atomic_dec(&starget->target_busy); > + if (starget->can_queue > 0) > + atomic_dec(&starget->target_busy); > > if (unlikely(scsi_host_in_recovery(shost) && > (shost->host_failed || shost->host_eh_scheduled))) { > @@ -1335,6 +1336,9 @@ static inline int scsi_target_queue_ready(struc= t Scsi_Host *shost, > spin_unlock_irq(shost->host_lock); > } > > + if (starget->can_queue <=3D 0) > + return 1; > + > busy =3D atomic_inc_return(&starget->target_busy) - 1; > if (busy =3D=3D 0 && atomic_read(&starget->target_blocked) > 0) { > if (atomic_dec_return(&starget->target_blocked) > 0) > @@ -1344,7 +1348,7 @@ static inline int scsi_target_queue_ready(struc= t Scsi_Host *shost, > "unblocking target at zero depth\n")); > } > > - if (starget->can_queue > 0 && busy >=3D starget->can_queue) > + if (busy >=3D starget->can_queue) > goto starved; > if (atomic_read(&starget->target_blocked) > 0) > goto starved; > @@ -1356,7 +1360,8 @@ starved: > list_move_tail(&sdev->starved_entry, &shost->starved_list); > spin_unlock_irq(shost->host_lock); > out_dec: > - atomic_dec(&starget->target_busy); > + if (starget->can_queue > 0) > + atomic_dec(&starget->target_busy); > return 0; > } > > @@ -1473,7 +1478,8 @@ static void scsi_kill_request(struct request *r= eq, struct request_queue *q) > */ > atomic_inc(&sdev->device_busy); > atomic_inc(&shost->host_busy); > - atomic_inc(&starget->target_busy); > + if (starget->can_queue > 0) > + atomic_inc(&starget->target_busy); > > blk_complete_request(req); > } > @@ -1642,7 +1648,8 @@ static void scsi_request_fn(struct request_queu= e *q) > return; > > host_not_ready: > - atomic_dec(&scsi_target(sdev)->target_busy); > + if (scsi_target(sdev)->can_queue > 0) > + atomic_dec(&scsi_target(sdev)->target_busy); > not_ready: > /* > * lock q, handle tag, requeue req, and decrement device_busy. We > Hmm. 'can_queue' can be changed by the LLDD. Don't we need some sort=20 of synchronization here? (Or move that to atomic_t, too?) Cheers, Hannes --=20 Dr. Hannes Reinecke zSeries & Storage hare@suse.de +49 911 74053 688 SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 N=FCrnberg GF: J. Hawn, J. Guild, F. Imend=F6rffer, HRB 16746 (AG N=FCrnberg)