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Date: Wed, 09 Jul 2014 13:15:58 +0200
From: Hannes Reinecke <hare@...e.de>
To: Christoph Hellwig <hch@....de>,
James Bottomley <James.Bottomley@...senPartnership.com>
CC: Jens Axboe <axboe@...nel.dk>,
Bart Van Assche <bvanassche@...ionio.com>,
Robert Elliott <Elliott@...com>, linux-scsi@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH 07/14] scsi: convert host_busy to atomic_t
On 06/25/2014 06:51 PM, Christoph Hellwig wrote:
> Avoid taking the host-wide host_lock to check the per-host 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@....de>
> ---
> drivers/scsi/advansys.c | 4 +-
> drivers/scsi/libiscsi.c | 4 +-
> drivers/scsi/libsas/sas_scsi_host.c | 5 ++-
> drivers/scsi/qlogicpti.c | 2 +-
> drivers/scsi/scsi.c | 2 +-
> drivers/scsi/scsi_error.c | 7 ++--
> drivers/scsi/scsi_lib.c | 71 +++++++++++++++++++++--------------
> drivers/scsi/scsi_sysfs.c | 9 ++++-
> include/scsi/scsi_host.h | 10 ++---
> 9 files changed, 66 insertions(+), 48 deletions(-)
>
> diff --git a/drivers/scsi/advansys.c b/drivers/scsi/advansys.c
> index e716d0a..43761c1 100644
> --- a/drivers/scsi/advansys.c
> +++ b/drivers/scsi/advansys.c
> @@ -2512,7 +2512,7 @@ static void asc_prt_scsi_host(struct Scsi_Host *s)
>
> printk("Scsi_Host at addr 0x%p, device %s\n", s, dev_name(boardp->dev));
> printk(" host_busy %u, host_no %d,\n",
> - s->host_busy, s->host_no);
> + atomic_read(&s->host_busy), s->host_no);
>
> printk(" base 0x%lx, io_port 0x%lx, irq %d,\n",
> (ulong)s->base, (ulong)s->io_port, boardp->irq);
> @@ -3346,7 +3346,7 @@ static void asc_prt_driver_conf(struct seq_file *m, struct Scsi_Host *shost)
>
> seq_printf(m,
> " host_busy %u, max_id %u, max_lun %llu, max_channel %u\n",
> - shost->host_busy, shost->max_id,
> + atomic_read(&shost->host_busy), shost->max_id,
> shost->max_lun, shost->max_channel);
>
> seq_printf(m,
> diff --git a/drivers/scsi/libiscsi.c b/drivers/scsi/libiscsi.c
> index f2db82b..f9f3a12 100644
> --- a/drivers/scsi/libiscsi.c
> +++ b/drivers/scsi/libiscsi.c
> @@ -2971,7 +2971,7 @@ void iscsi_conn_teardown(struct iscsi_cls_conn *cls_conn)
> */
> for (;;) {
> spin_lock_irqsave(session->host->host_lock, flags);
> - if (!session->host->host_busy) { /* OK for ERL == 0 */
> + if (!atomic_read(&session->host->host_busy)) { /* OK for ERL == 0 */
> spin_unlock_irqrestore(session->host->host_lock, flags);
> break;
> }
> @@ -2979,7 +2979,7 @@ void iscsi_conn_teardown(struct iscsi_cls_conn *cls_conn)
> msleep_interruptible(500);
> iscsi_conn_printk(KERN_INFO, conn, "iscsi conn_destroy(): "
> "host_busy %d host_failed %d\n",
> - session->host->host_busy,
> + atomic_read(&session->host->host_busy),
> session->host->host_failed);
> /*
> * force eh_abort() to unblock
> diff --git a/drivers/scsi/libsas/sas_scsi_host.c b/drivers/scsi/libsas/sas_scsi_host.c
> index 7d02a19..24e477d 100644
> --- a/drivers/scsi/libsas/sas_scsi_host.c
> +++ b/drivers/scsi/libsas/sas_scsi_host.c
> @@ -813,7 +813,7 @@ retry:
> spin_unlock_irq(shost->host_lock);
>
> SAS_DPRINTK("Enter %s busy: %d failed: %d\n",
> - __func__, shost->host_busy, shost->host_failed);
> + __func__, atomic_read(&shost->host_busy), shost->host_failed);
> /*
> * Deal with commands that still have SAS tasks (i.e. they didn't
> * complete via the normal sas_task completion mechanism),
> @@ -858,7 +858,8 @@ out:
> goto retry;
>
> SAS_DPRINTK("--- Exit %s: busy: %d failed: %d tries: %d\n",
> - __func__, shost->host_busy, shost->host_failed, tries);
> + __func__, atomic_read(&shost->host_busy),
> + shost->host_failed, tries);
> }
>
> enum blk_eh_timer_return sas_scsi_timed_out(struct scsi_cmnd *cmd)
> diff --git a/drivers/scsi/qlogicpti.c b/drivers/scsi/qlogicpti.c
> index 6d48d30..740ae49 100644
> --- a/drivers/scsi/qlogicpti.c
> +++ b/drivers/scsi/qlogicpti.c
> @@ -959,7 +959,7 @@ static inline void update_can_queue(struct Scsi_Host *host, u_int in_ptr, u_int
> /* Temporary workaround until bug is found and fixed (one bug has been found
> already, but fixing it makes things even worse) -jj */
> int num_free = QLOGICPTI_REQ_QUEUE_LEN - REQ_QUEUE_DEPTH(in_ptr, out_ptr) - 64;
> - host->can_queue = host->host_busy + num_free;
> + host->can_queue = atomic_read(&host->host_busy) + num_free;
> host->sg_tablesize = QLOGICPTI_MAX_SG(num_free);
> }
>
> diff --git a/drivers/scsi/scsi.c b/drivers/scsi/scsi.c
> index d3bd6cf..35a23e2 100644
> --- a/drivers/scsi/scsi.c
> +++ b/drivers/scsi/scsi.c
> @@ -603,7 +603,7 @@ void scsi_log_completion(struct scsi_cmnd *cmd, int disposition)
> if (level > 3)
> scmd_printk(KERN_INFO, cmd,
> "scsi host busy %d failed %d\n",
> - cmd->device->host->host_busy,
> + atomic_read(&cmd->device->host->host_busy),
> cmd->device->host->host_failed);
> }
> }
> diff --git a/drivers/scsi/scsi_error.c b/drivers/scsi/scsi_error.c
> index e4a5324..5db8454 100644
> --- a/drivers/scsi/scsi_error.c
> +++ b/drivers/scsi/scsi_error.c
> @@ -59,7 +59,7 @@ static int scsi_try_to_abort_cmd(struct scsi_host_template *,
> /* called with shost->host_lock held */
> void scsi_eh_wakeup(struct Scsi_Host *shost)
> {
> - if (shost->host_busy == shost->host_failed) {
> + if (atomic_read(&shost->host_busy) == shost->host_failed) {
> trace_scsi_eh_wakeup(shost);
> wake_up_process(shost->ehandler);
> SCSI_LOG_ERROR_RECOVERY(5, shost_printk(KERN_INFO, shost,
> @@ -2164,7 +2164,7 @@ int scsi_error_handler(void *data)
> while (!kthread_should_stop()) {
> set_current_state(TASK_INTERRUPTIBLE);
> if ((shost->host_failed == 0 && shost->host_eh_scheduled == 0) ||
> - shost->host_failed != shost->host_busy) {
> + shost->host_failed != atomic_read(&shost->host_busy)) {
> SCSI_LOG_ERROR_RECOVERY(1,
> shost_printk(KERN_INFO, shost,
> "scsi_eh_%d: sleeping\n",
> @@ -2178,7 +2178,8 @@ int scsi_error_handler(void *data)
> shost_printk(KERN_INFO, shost,
> "scsi_eh_%d: waking up %d/%d/%d\n",
> shost->host_no, shost->host_eh_scheduled,
> - shost->host_failed, shost->host_busy));
> + shost->host_failed,
> + atomic_read(&shost->host_busy)));
>
> /*
> * We have a host that is failing for some reason. Figure out
> diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
> index 5e269d6..5d37d79 100644
> --- a/drivers/scsi/scsi_lib.c
> +++ b/drivers/scsi/scsi_lib.c
> @@ -292,14 +292,17 @@ void scsi_device_unbusy(struct scsi_device *sdev)
> struct scsi_target *starget = scsi_target(sdev);
> unsigned long flags;
>
> - spin_lock_irqsave(shost->host_lock, flags);
> - shost->host_busy--;
> + atomic_dec(&shost->host_busy);
> atomic_dec(&starget->target_busy);
> +
> if (unlikely(scsi_host_in_recovery(shost) &&
> - (shost->host_failed || shost->host_eh_scheduled)))
> + (shost->host_failed || shost->host_eh_scheduled))) {
> + spin_lock_irqsave(shost->host_lock, flags);
> scsi_eh_wakeup(shost);
> - spin_unlock(shost->host_lock);
> - spin_lock(sdev->request_queue->queue_lock);
> + 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);
> }
> @@ -367,7 +370,8 @@ static inline int scsi_target_is_busy(struct scsi_target *starget)
>
> static inline int scsi_host_is_busy(struct Scsi_Host *shost)
> {
> - if ((shost->can_queue > 0 && shost->host_busy >= shost->can_queue) ||
> + if ((shost->can_queue > 0 &&
> + atomic_read(&shost->host_busy) >= shost->can_queue) ||
> shost->host_blocked || shost->host_self_blocked)
> return 1;
>
> @@ -1359,38 +1363,51 @@ static inline int scsi_host_queue_ready(struct request_queue *q,
> struct Scsi_Host *shost,
> struct scsi_device *sdev)
> {
> - int ret = 0;
> -
> - spin_lock_irq(shost->host_lock);
> + unsigned int busy;
>
> if (scsi_host_in_recovery(shost))
> - goto out;
> - if (shost->host_busy == 0 && shost->host_blocked) {
> + return 0;
> +
> + busy = atomic_inc_return(&shost->host_busy) - 1;
> + if (busy == 0 && shost->host_blocked) {
> /*
> * unblock after host_blocked iterates to zero
> */
> - if (--shost->host_blocked != 0)
> - goto out;
> + spin_lock_irq(shost->host_lock);
> + if (--shost->host_blocked != 0) {
> + spin_unlock_irq(shost->host_lock);
> + goto out_dec;
> + }
> + spin_unlock_irq(shost->host_lock);
>
> SCSI_LOG_MLQUEUE(3,
> shost_printk(KERN_INFO, shost,
> "unblocking host at zero depth\n"));
> }
> - if (scsi_host_is_busy(shost)) {
> - if (list_empty(&sdev->starved_entry))
> - list_add_tail(&sdev->starved_entry, &shost->starved_list);
> - goto out;
> - }
> +
> + if (shost->can_queue > 0 && busy >= shost->can_queue)
> + goto starved;
> + if (shost->host_blocked || shost->host_self_blocked)
> + goto starved;
>
> /* We're OK to process the command, so we can't be starved */
> - if (!list_empty(&sdev->starved_entry))
> - list_del_init(&sdev->starved_entry);
> + if (!list_empty(&sdev->starved_entry)) {
> + spin_lock_irq(shost->host_lock);
> + if (!list_empty(&sdev->starved_entry))
> + list_del_init(&sdev->starved_entry);
> + spin_unlock_irq(shost->host_lock);
> + }
>
> - shost->host_busy++;
> - ret = 1;
> -out:
> + return 1;
> +
> +starved:
> + spin_lock_irq(shost->host_lock);
> + if (list_empty(&sdev->starved_entry))
> + list_add_tail(&sdev->starved_entry, &shost->starved_list);
> spin_unlock_irq(shost->host_lock);
> - return ret;
> +out_dec:
> + atomic_dec(&shost->host_busy);
> + return 0;
> }
>
> /*
> @@ -1454,12 +1471,8 @@ static void scsi_kill_request(struct request *req, struct request_queue *q)
> * with the locks as normal issue path does.
> */
> sdev->device_busy++;
> - spin_unlock(sdev->request_queue->queue_lock);
> - spin_lock(shost->host_lock);
> - shost->host_busy++;
> + atomic_inc(&shost->host_busy);
> atomic_inc(&starget->target_busy);
> - spin_unlock(shost->host_lock);
> - spin_lock(sdev->request_queue->queue_lock);
>
> blk_complete_request(req);
> }
> diff --git a/drivers/scsi/scsi_sysfs.c b/drivers/scsi/scsi_sysfs.c
> index 5f36788..7ec5e06 100644
> --- a/drivers/scsi/scsi_sysfs.c
> +++ b/drivers/scsi/scsi_sysfs.c
> @@ -334,7 +334,6 @@ store_shost_eh_deadline(struct device *dev, struct device_attribute *attr,
> static DEVICE_ATTR(eh_deadline, S_IRUGO | S_IWUSR, show_shost_eh_deadline, store_shost_eh_deadline);
>
> shost_rd_attr(unique_id, "%u\n");
> -shost_rd_attr(host_busy, "%hu\n");
> shost_rd_attr(cmd_per_lun, "%hd\n");
> shost_rd_attr(can_queue, "%hd\n");
> shost_rd_attr(sg_tablesize, "%hu\n");
> @@ -344,6 +343,14 @@ shost_rd_attr(prot_capabilities, "%u\n");
> shost_rd_attr(prot_guard_type, "%hd\n");
> shost_rd_attr2(proc_name, hostt->proc_name, "%s\n");
>
> +static ssize_t
> +show_host_busy(struct device *dev, struct device_attribute *attr, char *buf)
> +{
> + struct Scsi_Host *shost = class_to_shost(dev);
> + return snprintf(buf, 20, "%hu\n", atomic_read(&shost->host_busy));
> +}
> +static DEVICE_ATTR(host_busy, S_IRUGO, show_host_busy, NULL);
> +
> static struct attribute *scsi_sysfs_shost_attrs[] = {
> &dev_attr_unique_id.attr,
> &dev_attr_host_busy.attr,
> diff --git a/include/scsi/scsi_host.h b/include/scsi/scsi_host.h
> index abb6958..3d124f7 100644
> --- a/include/scsi/scsi_host.h
> +++ b/include/scsi/scsi_host.h
> @@ -603,13 +603,9 @@ struct Scsi_Host {
> */
> struct blk_queue_tag *bqt;
>
> - /*
> - * The following two fields are protected with host_lock;
> - * however, eh routines can safely access during eh processing
> - * without acquiring the lock.
> - */
> - unsigned int host_busy; /* commands actually active on low-level */
> - unsigned int host_failed; /* commands that failed. */
> + atomic_t host_busy; /* commands actually active on low-level */
> + unsigned int host_failed; /* commands that failed.
> + protected by host_lock */
> unsigned int host_eh_scheduled; /* EH scheduled without command */
>
> unsigned int host_no; /* Used for IOCTL_GET_IDLUN, /proc/scsi et al. */
>
Reviewed-by: Hannes Reinecke <hare@...e.de>
Cheers,
Hannes
--
Dr. Hannes Reinecke zSeries & Storage
hare@...e.de +49 911 74053 688
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: J. Hawn, J. Guild, F. Imendörffer, HRB 16746 (AG Nürnberg)
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