From 71e75c97f97a9645d25fbf3d8e4165a558f18747 Mon Sep 17 00:00:00 2001 From: Christoph Hellwig Date: Fri, 11 Apr 2014 19:07:01 +0200 Subject: [PATCH] scsi: convert device_busy to atomic_t Avoid taking the queue_lock to check the per-device queue limit. Instead we do an atomic_inc_return early on to grab our slot in the queue, and if necessary decrement it after finishing all checks. Unlike the host and target busy counters this doesn't allow us to avoid the queue_lock in the request_fn due to the way the interface works, but it'll allow us to prepare for using the blk-mq code, which doesn't use the queue_lock at all, and it at least avoids a queue_lock round trip in scsi_device_unbusy, which is still important given how busy the queue_lock is. Signed-off-by: Christoph Hellwig Reviewed-by: Hannes Reinecke Reviewed-by: Webb Scales Acked-by: Jens Axboe Tested-by: Bart Van Assche Tested-by: Robert Elliott --- drivers/message/fusion/mptsas.c | 2 +- drivers/scsi/scsi_lib.c | 50 ++++++++++++++++++--------------- drivers/scsi/scsi_sysfs.c | 10 ++++++- drivers/scsi/sg.c | 2 +- include/scsi/scsi_device.h | 4 +-- 5 files changed, 40 insertions(+), 28 deletions(-) diff --git a/drivers/message/fusion/mptsas.c b/drivers/message/fusion/mptsas.c index 711fcb5cec8..d636dbe172a 100644 --- a/drivers/message/fusion/mptsas.c +++ b/drivers/message/fusion/mptsas.c @@ -3763,7 +3763,7 @@ mptsas_send_link_status_event(struct fw_event_work *fw_event) printk(MYIOC_s_DEBUG_FMT "SDEV OUTSTANDING CMDS" "%d\n", ioc->name, - sdev->device_busy)); + atomic_read(&sdev->device_busy))); } } diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c index d0bd7e0ab7a..1ddf0fb43b5 100644 --- a/drivers/scsi/scsi_lib.c +++ b/drivers/scsi/scsi_lib.c @@ -302,9 +302,7 @@ void scsi_device_unbusy(struct scsi_device *sdev) spin_unlock_irqrestore(shost->host_lock, flags); } - spin_lock_irqsave(sdev->request_queue->queue_lock, flags); - sdev->device_busy--; - spin_unlock_irqrestore(sdev->request_queue->queue_lock, flags); + atomic_dec(&sdev->device_busy); } /* @@ -355,9 +353,9 @@ static void scsi_single_lun_run(struct scsi_device *current_sdev) static inline int scsi_device_is_busy(struct scsi_device *sdev) { - if (sdev->device_busy >= sdev->queue_depth || sdev->device_blocked) + if (atomic_read(&sdev->device_busy) >= sdev->queue_depth || + sdev->device_blocked) return 1; - return 0; } @@ -1204,7 +1202,7 @@ scsi_prep_return(struct request_queue *q, struct request *req, int ret) * queue must be restarted, so we schedule a callback to happen * shortly. */ - if (sdev->device_busy == 0) + if (atomic_read(&sdev->device_busy) == 0) blk_delay_queue(q, SCSI_QUEUE_DELAY); break; default: @@ -1255,26 +1253,33 @@ static void scsi_unprep_fn(struct request_queue *q, struct request *req) static inline int scsi_dev_queue_ready(struct request_queue *q, struct scsi_device *sdev) { - if (sdev->device_busy == 0 && sdev->device_blocked) { + unsigned int busy; + + busy = atomic_inc_return(&sdev->device_busy) - 1; + if (sdev->device_blocked) { + if (busy) + goto out_dec; + /* * unblock after device_blocked iterates to zero */ - if (--sdev->device_blocked == 0) { - SCSI_LOG_MLQUEUE(3, - sdev_printk(KERN_INFO, sdev, - "unblocking device at zero depth\n")); - } else { + if (--sdev->device_blocked != 0) { blk_delay_queue(q, SCSI_QUEUE_DELAY); - return 0; + goto out_dec; } + SCSI_LOG_MLQUEUE(3, sdev_printk(KERN_INFO, sdev, + "unblocking device at zero depth\n")); } - if (scsi_device_is_busy(sdev)) - return 0; + + if (busy >= sdev->queue_depth) + goto out_dec; return 1; +out_dec: + atomic_dec(&sdev->device_busy); + return 0; } - /* * scsi_target_queue_ready: checks if there we can send commands to target * @sdev: scsi device on starget to check. @@ -1448,7 +1453,7 @@ static void scsi_kill_request(struct request *req, struct request_queue *q) * bump busy counts. To bump the counters, we need to dance * with the locks as normal issue path does. */ - sdev->device_busy++; + atomic_inc(&sdev->device_busy); atomic_inc(&shost->host_busy); atomic_inc(&starget->target_busy); @@ -1544,7 +1549,7 @@ static void scsi_request_fn(struct request_queue *q) * accept it. */ req = blk_peek_request(q); - if (!req || !scsi_dev_queue_ready(q, sdev)) + if (!req) break; if (unlikely(!scsi_device_online(sdev))) { @@ -1554,13 +1559,14 @@ static void scsi_request_fn(struct request_queue *q) continue; } + if (!scsi_dev_queue_ready(q, sdev)) + break; /* * Remove the request from the request list. */ if (!(blk_queue_tagged(q) && !blk_queue_start_tag(q, req))) blk_start_request(req); - sdev->device_busy++; spin_unlock_irq(q->queue_lock); cmd = req->special; @@ -1630,9 +1636,9 @@ static void scsi_request_fn(struct request_queue *q) */ spin_lock_irq(q->queue_lock); blk_requeue_request(q, req); - sdev->device_busy--; + atomic_dec(&sdev->device_busy); out_delay: - if (sdev->device_busy == 0 && !scsi_device_blocked(sdev)) + if (atomic_read(&sdev->device_busy) && !scsi_device_blocked(sdev)) blk_delay_queue(q, SCSI_QUEUE_DELAY); } @@ -2371,7 +2377,7 @@ scsi_device_quiesce(struct scsi_device *sdev) return err; scsi_run_queue(sdev->request_queue); - while (sdev->device_busy) { + while (atomic_read(&sdev->device_busy)) { msleep_interruptible(200); scsi_run_queue(sdev->request_queue); } diff --git a/drivers/scsi/scsi_sysfs.c b/drivers/scsi/scsi_sysfs.c index de57b8bca7b..79df9847ede 100644 --- a/drivers/scsi/scsi_sysfs.c +++ b/drivers/scsi/scsi_sysfs.c @@ -585,13 +585,21 @@ static int scsi_sdev_check_buf_bit(const char *buf) * Create the actual show/store functions and data structures. */ sdev_rd_attr (device_blocked, "%d\n"); -sdev_rd_attr (device_busy, "%d\n"); sdev_rd_attr (type, "%d\n"); sdev_rd_attr (scsi_level, "%d\n"); sdev_rd_attr (vendor, "%.8s\n"); sdev_rd_attr (model, "%.16s\n"); sdev_rd_attr (rev, "%.4s\n"); +static ssize_t +sdev_show_device_busy(struct device *dev, struct device_attribute *attr, + char *buf) +{ + struct scsi_device *sdev = to_scsi_device(dev); + return snprintf(buf, 20, "%d\n", atomic_read(&sdev->device_busy)); +} +static DEVICE_ATTR(device_busy, S_IRUGO, sdev_show_device_busy, NULL); + /* * TODO: can we make these symlinks to the block layer ones? */ diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c index 7a291f5c722..01cf8888879 100644 --- a/drivers/scsi/sg.c +++ b/drivers/scsi/sg.c @@ -2574,7 +2574,7 @@ static int sg_proc_seq_show_dev(struct seq_file *s, void *v) scsidp->id, scsidp->lun, (int) scsidp->type, 1, (int) scsidp->queue_depth, - (int) scsidp->device_busy, + (int) atomic_read(&scsidp->device_busy), (int) scsi_device_online(scsidp)); } read_unlock_irqrestore(&sg_index_lock, iflags); diff --git a/include/scsi/scsi_device.h b/include/scsi/scsi_device.h index 4e078b63a9e..3329901c724 100644 --- a/include/scsi/scsi_device.h +++ b/include/scsi/scsi_device.h @@ -81,9 +81,7 @@ struct scsi_device { struct list_head siblings; /* list of all devices on this host */ struct list_head same_target_siblings; /* just the devices sharing same target id */ - /* this is now protected by the request_queue->queue_lock */ - unsigned int device_busy; /* commands actually active on - * low-level. protected by queue_lock. */ + atomic_t device_busy; /* commands actually active on LLDD */ spinlock_t list_lock; struct list_head cmd_list; /* queue of in use SCSI Command structures */ struct list_head starved_entry; -- 2.41.0