From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932262AbaGILTq (ORCPT ); Wed, 9 Jul 2014 07:19:46 -0400 Received: from cantor2.suse.de ([195.135.220.15]:41663 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932237AbaGILTn (ORCPT ); Wed, 9 Jul 2014 07:19:43 -0400 Message-ID: <53BD254D.4000806@suse.de> Date: Wed, 09 Jul 2014 13:19:41 +0200 From: Hannes Reinecke User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.6.0 MIME-Version: 1.0 To: Christoph Hellwig , James Bottomley CC: Jens Axboe , Bart Van Assche , Robert Elliott , linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 10/14] scsi: only maintain target_blocked if the driver has a target queue limit References: <1403715121-1201-1-git-send-email-hch@lst.de> <1403715121-1201-11-git-send-email-hch@lst.de> In-Reply-To: <1403715121-1201-11-git-send-email-hch@lst.de> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@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 completion > for the usual case where the driver doesn't set a per-target can_queue > 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(struct Scsi_Host *shost, > spin_unlock_irq(shost->host_lock); > } > > + if (starget->can_queue <= 0) > + return 1; > + > busy = atomic_inc_return(&starget->target_busy) - 1; > if (busy == 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(struct Scsi_Host *shost, > "unblocking target at zero depth\n")); > } > > - if (starget->can_queue > 0 && busy >= starget->can_queue) > + if (busy >= 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 *req, 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_queue *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 of synchronization here? (Or move that to atomic_t, too?) 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)