From a488e74976bf0a9bccecdd094378394942dacef1 Mon Sep 17 00:00:00 2001 From: Jens Axboe Date: Fri, 16 Apr 2010 21:13:15 +0200 Subject: scsi: convert to blk_delay_queue() It was always abuse to reuse the plugging infrastructure for this, convert it to the (new) real API for delaying queueing a bit. A default delay of 3 msec is defined, to match the previous behaviour. Signed-off-by: Jens Axboe --- drivers/scsi/scsi_lib.c | 44 +++++++++++++++++++------------------------- 1 file changed, 19 insertions(+), 25 deletions(-) (limited to 'drivers/scsi/scsi_lib.c') diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c index 9045c52abd25..5a0ae7a944ce 100644 --- a/drivers/scsi/scsi_lib.c +++ b/drivers/scsi/scsi_lib.c @@ -67,6 +67,13 @@ static struct scsi_host_sg_pool scsi_sg_pools[] = { struct kmem_cache *scsi_sdb_cache; +/* + * When to reinvoke queueing after a resource shortage. It's 3 msecs to + * not change behaviour from the previous unplug mechanism, experimentation + * may prove this needs changing. + */ +#define SCSI_QUEUE_DELAY 3 + static void scsi_run_queue(struct request_queue *q); /* @@ -149,14 +156,7 @@ static int __scsi_queue_insert(struct scsi_cmnd *cmd, int reason, int unbusy) /* * Requeue this command. It will go before all other commands * that are already in the queue. - * - * NOTE: there is magic here about the way the queue is plugged if - * we have no outstanding commands. - * - * Although we *don't* plug the queue, we call the request - * function. The SCSI request function detects the blocked condition - * and plugs the queue appropriately. - */ + */ spin_lock_irqsave(q->queue_lock, flags); blk_requeue_request(q, cmd->request); spin_unlock_irqrestore(q->queue_lock, flags); @@ -1194,11 +1194,11 @@ int scsi_prep_return(struct request_queue *q, struct request *req, int ret) case BLKPREP_DEFER: /* * If we defer, the blk_peek_request() returns NULL, but the - * queue must be restarted, so we plug here if no returning - * command will automatically do that. + * queue must be restarted, so we schedule a callback to happen + * shortly. */ if (sdev->device_busy == 0) - blk_plug_device(q); + blk_delay_queue(q, SCSI_QUEUE_DELAY); break; default: req->cmd_flags |= REQ_DONTPREP; @@ -1237,7 +1237,7 @@ static inline int scsi_dev_queue_ready(struct request_queue *q, sdev_printk(KERN_INFO, sdev, "unblocking device at zero depth\n")); } else { - blk_plug_device(q); + blk_delay_queue(q, SCSI_QUEUE_DELAY); return 0; } } @@ -1467,7 +1467,7 @@ static void scsi_request_fn(struct request_queue *q) * the host is no longer able to accept any more requests. */ shost = sdev->host; - while (!blk_queue_plugged(q)) { + for (;;) { int rtn; /* * get next queueable request. We do this early to make sure @@ -1546,15 +1546,8 @@ static void scsi_request_fn(struct request_queue *q) */ rtn = scsi_dispatch_cmd(cmd); spin_lock_irq(q->queue_lock); - if(rtn) { - /* we're refusing the command; because of - * the way locks get dropped, we need to - * check here if plugging is required */ - if(sdev->device_busy == 0) - blk_plug_device(q); - - break; - } + if (rtn) + goto out_delay; } goto out; @@ -1573,9 +1566,10 @@ static void scsi_request_fn(struct request_queue *q) spin_lock_irq(q->queue_lock); blk_requeue_request(q, req); sdev->device_busy--; - if(sdev->device_busy == 0) - blk_plug_device(q); - out: +out_delay: + if (sdev->device_busy == 0) + blk_delay_queue(q, SCSI_QUEUE_DELAY); +out: /* must be careful here...if we trigger the ->remove() function * we cannot be holding the q lock */ spin_unlock_irq(q->queue_lock); -- cgit v1.2.3 From 24ecfbe27f65563909b14492afda2f1c21f7c044 Mon Sep 17 00:00:00 2001 From: Christoph Hellwig Date: Mon, 18 Apr 2011 11:41:33 +0200 Subject: block: add blk_run_queue_async Instead of overloading __blk_run_queue to force an offload to kblockd add a new blk_run_queue_async helper to do it explicitly. I've kept the blk_queue_stopped check for now, but I suspect it's not needed as the check we do when the workqueue items runs should be enough. Signed-off-by: Christoph Hellwig Signed-off-by: Jens Axboe --- drivers/scsi/scsi_lib.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'drivers/scsi/scsi_lib.c') diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c index 6d5c7ff43f5b..ab55c2fa7ce2 100644 --- a/drivers/scsi/scsi_lib.c +++ b/drivers/scsi/scsi_lib.c @@ -443,7 +443,7 @@ static void scsi_run_queue(struct request_queue *q) &sdev->request_queue->queue_flags); if (flagset) queue_flag_set(QUEUE_FLAG_REENTER, sdev->request_queue); - __blk_run_queue(sdev->request_queue, false); + __blk_run_queue(sdev->request_queue); if (flagset) queue_flag_clear(QUEUE_FLAG_REENTER, sdev->request_queue); spin_unlock(sdev->request_queue->queue_lock); -- cgit v1.2.3 From c21e6beba8835d09bb80e34961430b13e60381c5 Mon Sep 17 00:00:00 2001 From: Jens Axboe Date: Tue, 19 Apr 2011 13:32:46 +0200 Subject: block: get rid of QUEUE_FLAG_REENTER We are currently using this flag to check whether it's safe to call into ->request_fn(). If it is set, we punt to kblockd. But we get a lot of false positives and excessive punts to kblockd, which hurts performance. The only real abuser of this infrastructure is SCSI. So export the async queue run and convert SCSI over to use that. There's room for improvement in that SCSI need not always use the async call, but this fixes our performance issue and they can fix that up in due time. Signed-off-by: Jens Axboe --- drivers/scsi/scsi_lib.c | 17 +---------------- 1 file changed, 1 insertion(+), 16 deletions(-) (limited to 'drivers/scsi/scsi_lib.c') diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c index ab55c2fa7ce2..e9901b8f8443 100644 --- a/drivers/scsi/scsi_lib.c +++ b/drivers/scsi/scsi_lib.c @@ -411,8 +411,6 @@ static void scsi_run_queue(struct request_queue *q) list_splice_init(&shost->starved_list, &starved_list); while (!list_empty(&starved_list)) { - int flagset; - /* * As long as shost is accepting commands and we have * starved queues, call blk_run_queue. scsi_request_fn @@ -435,20 +433,7 @@ static void scsi_run_queue(struct request_queue *q) continue; } - spin_unlock(shost->host_lock); - - spin_lock(sdev->request_queue->queue_lock); - flagset = test_bit(QUEUE_FLAG_REENTER, &q->queue_flags) && - !test_bit(QUEUE_FLAG_REENTER, - &sdev->request_queue->queue_flags); - if (flagset) - queue_flag_set(QUEUE_FLAG_REENTER, sdev->request_queue); - __blk_run_queue(sdev->request_queue); - if (flagset) - queue_flag_clear(QUEUE_FLAG_REENTER, sdev->request_queue); - spin_unlock(sdev->request_queue->queue_lock); - - spin_lock(shost->host_lock); + blk_run_queue_async(sdev->request_queue); } /* put any unprocessed entries back */ list_splice(&starved_list, &shost->starved_list); -- cgit v1.2.3