[PATCH 07/14] scsi: convert host_busy to atomic_t

From: Christoph Hellwig
Date: Thu Jun 12 2014 - 09:47:16 EST

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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@xxxxxx>
---
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 | 6 +--
drivers/scsi/scsi_lib.c | 71 +++++++++++++++++++++--------------
drivers/scsi/scsi_sysfs.c | 9 ++++-
include/scsi/scsi_host.h | 10 ++---
9 files changed, 65 insertions(+), 48 deletions(-)

diff --git a/drivers/scsi/advansys.c b/drivers/scsi/advansys.c
index d814588..0a6ecbd 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 %u, 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 ecd7bd3..f4e9215 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 25d0f12..eec31b0 100644
--- a/drivers/scsi/libsas/sas_scsi_host.c
+++ b/drivers/scsi/libsas/sas_scsi_host.c
@@ -812,7 +812,7 @@ 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),
@@ -857,7 +857,8 @@ 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 8ca9ed2..091329a 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 cbe38e5..3dae321 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,
@@ -2155,7 +2155,7 @@ 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,
printk("scsi_eh_%d: sleeping\n",
shost->host_no));
@@ -2167,7 +2167,7 @@ int scsi_error_handler(void *data)
SCSI_LOG_ERROR_RECOVERY(1,
printk("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 9e288e6..3f51bb8 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,
printk("scsi%d unblocking host at zero depth\n",
shost->host_no));
}
- 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 074e8cc..f489934 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 94844fc..590e1af 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. */
--
1.7.10.4

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