On Thursday 19 February 2009 07:41:18 Alasdair G Kergon wrote:
> On Tue, Feb 17, 2009 at 07:17:37PM +0530, Nikanth Karthikesan wrote:
> > Delay retry to activate_path if it returns SCSI_DH_RETRY.
>
> Please write a complete patch header if you'd like this queued for
> upstream!
>
> E.g. Why? Any cases where this will make matters worse or make no
> difference?
>
Sorry for the terse changelog.
> > + unsigned long pg_init_jiffy; /* To delay retry if SCSI_DH_RETRY */
> > +#define SCSI_DH_RETRY_DELAY ((HZ * 2))
>
> Why that particular value?
There is no specific reason. Just picked 2 seconds based on the TODO comment,
"For SCSI_DH_RETRY we should wait a couple seconds".
> Please move it into a header file with an explanation of what it does.
>
done.
Attached is the patch with comments from you and Chandra incorporated.
Thanks
Nikanth
SCSI Device Handlers return SCSI_DH_IMM_RETRY if we could retry
immediately and SCSI_DH_RETRY in cases where it is better to retry
after some delay.
Currently we retry immediately irrespective of SCSI_DH_IMM_RETRY and
SCSI_DH_RETRY. This patch adds a 2 second delay before retrying to
activate a device, if it returns SCSI_DH_RETRY.
Signed-off-by: Nikanth Karthikesan <knikanth@xxxxxxx>
---
diff --git a/drivers/md/dm-mpath.c b/drivers/md/dm-mpath.c
index 095f77b..6fd76f1 100644
--- a/drivers/md/dm-mpath.c
+++ b/drivers/md/dm-mpath.c
@@ -65,12 +65,13 @@ struct multipath {
spinlock_t lock;
const char *hw_handler_name;
- struct work_struct activate_path;
+ struct delayed_work activate_path;
struct pgpath *pgpath_to_activate;
unsigned nr_priority_groups;
struct list_head priority_groups;
unsigned pg_init_required; /* pg_init needs calling? */
unsigned pg_init_in_progress; /* Only one pg_init allowed at once */
+ unsigned pg_init_delay; /* delay required before retry? */
unsigned nr_valid_paths; /* Total number of usable paths */
struct pgpath *current_pgpath;
@@ -203,7 +204,7 @@ static struct multipath *alloc_multipath(struct dm_target *ti)
m->queue_io = 1;
INIT_WORK(&m->process_queued_ios, process_queued_ios);
INIT_WORK(&m->trigger_event, trigger_event);
- INIT_WORK(&m->activate_path, activate_path);
+ INIT_DELAYED_WORK(&m->activate_path, activate_path);
m->mpio_pool = mempool_create_slab_pool(MIN_IOS, _mpio_cache);
if (!m->mpio_pool) {
kfree(m);
@@ -431,6 +432,7 @@ static void process_queued_ios(struct work_struct *work)
struct pgpath *pgpath = NULL;
unsigned init_required = 0, must_queue = 1;
unsigned long flags;
+ unsigned long delay = 0;
spin_lock_irqsave(&m->lock, flags);
@@ -452,13 +454,15 @@ static void process_queued_ios(struct work_struct *work)
m->pg_init_required = 0;
m->pg_init_in_progress = 1;
init_required = 1;
+ if (m->pg_init_delay)
+ delay = SCSI_DH_RETRY_DELAY;
}
out:
spin_unlock_irqrestore(&m->lock, flags);
if (init_required)
- queue_work(kmpath_handlerd, &m->activate_path);
+ queue_delayed_work(kmpath_handlerd, &m->activate_path, delay);
if (!must_queue)
dispatch_queued_ios(m);
@@ -1060,6 +1064,7 @@ static void pg_init_done(struct dm_path *path, int errors)
struct priority_group *pg = pgpath->pg;
struct multipath *m = pg->m;
unsigned long flags;
+ unsigned delay = 0;
/* device or driver problems */
switch (errors) {
@@ -1084,8 +1089,11 @@ static void pg_init_done(struct dm_path *path, int errors)
*/
bypass_pg(m, pg, 1);
break;
- /* TODO: For SCSI_DH_RETRY we should wait a couple seconds */
+ /*
+ * For SCSI_DH_RETRY we wait before retrying.
+ */
case SCSI_DH_RETRY:
+ delay = 1;
case SCSI_DH_IMM_RETRY:
case SCSI_DH_RES_TEMP_UNAVAIL:
if (pg_init_limit_reached(m, pgpath))
@@ -1112,6 +1120,7 @@ static void pg_init_done(struct dm_path *path, int errors)
}
m->pg_init_in_progress = 0;
+ m->pg_init_delay = delay;
queue_work(kmultipathd, &m->process_queued_ios);
spin_unlock_irqrestore(&m->lock, flags);
}
@@ -1120,7 +1129,7 @@ static void activate_path(struct work_struct *work)
{
int ret;
struct multipath *m =
- container_of(work, struct multipath, activate_path);
+ container_of(work, struct multipath, activate_path.work);
struct dm_path *path;
unsigned long flags;
diff --git a/include/scsi/scsi_dh.h b/include/scsi/scsi_dh.h
index 33efce2..f099d86 100644
--- a/include/scsi/scsi_dh.h
+++ b/include/scsi/scsi_dh.h
@@ -55,6 +55,10 @@ enum {
SCSI_DH_NOSYS,
SCSI_DH_DRIVER_MAX,
};
+
+/* Time to wait before retry in case of SCSI_DH_RETRY */
+#define SCSI_DH_RETRY_DELAY ((HZ * 2))
+
#if defined(CONFIG_SCSI_DH) || defined(CONFIG_SCSI_DH_MODULE)
extern int scsi_dh_activate(struct request_queue *);
extern int scsi_dh_handler_exist(const char *);
--
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