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02-19-2009, 01:11 AM
Alasdair G Kergon
dm mpath: delay retry activate_path on SCSI_DH_RETRY
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?
> + unsigned long pg_init_jiffy; /* To delay retry if SCSI_DH_RETRY */
> +#define SCSI_DH_RETRY_DELAY ((HZ * 2))
Why that particular value?
Please move it into a header file with an explanation of what it does.
Alasdair
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02-19-2009, 06:10 AM
Nikanth Karthikesan
dm mpath: delay retry activate_path on SCSI_DH_RETRY
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.
I do not see the reason for this variable, you can as well put the delay
in pg_init_delay and use it directly (and set it to zero after using
it) ?
>
> 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;
You can get rid of this variable also and set it directly under
SCSI_DH_RETRY.
>
> /* 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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02-20-2009, 04:03 AM
Nikanth Karthikesan
dm mpath: delay retry activate_path on SCSI_DH_RETRY
On Friday 20 February 2009 06:15:29 Chandra Seetharaman wrote:
> On Thu, 2009-02-19 at 12:40 +0530, Nikanth Karthikesan wrote:
>
> <snip>
>
> > @@ -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;
>
> I do not see the reason for this variable, you can as well put the delay
> in pg_init_delay and use it directly (and set it to zero after using
> it) ?
>
I missed resetting pg_init_delay to zero after using it. I have attached the
corrected patch with this. This variable keeps the code cleaner(avoids taking
m->lock). Also having only a boolean in struct multipath keeps it a bit
smaller.
off-topic:
I think struct multipath can be shrunk even further by making various flags
like pg_init_required, pg_init_in_progress, queue_io, queue_if_no_path,
saved_queue_if_no_path in to a single variable. Thoughts?
<snip>
> > @@ -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;
>
> You can get rid of this variable also and set it directly under
> SCSI_DH_RETRY.
>
pg_init_delay is protected by the m->lock. And this variable helps in keeping
the code cleaner.
<snip>
I am attaching the fixed patch(resetting pg_init_delay to zero after using
it).
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.
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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02-20-2009, 02:08 PM
Konrad Rzeszutek
dm mpath: delay retry activate_path on SCSI_DH_RETRY
> off-topic:
> I think struct multipath can be shrunk even further by making various flags
> like pg_init_required, pg_init_in_progress, queue_io, queue_if_no_path,
> saved_queue_if_no_path in to a single variable. Thoughts?
Do the benefits (cut down on the size of the structure which is allocated once
for a map) vs readability worth it?
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02-20-2009, 08:11 PM
Chandra Seetharaman
dm mpath: delay retry activate_path on SCSI_DH_RETRY
On Fri, 2009-02-20 at 10:33 +0530, Nikanth Karthikesan wrote:
> On Friday 20 February 2009 06:15:29 Chandra Seetharaman wrote:
> > On Thu, 2009-02-19 at 12:40 +0530, Nikanth Karthikesan wrote:
> >
> > <snip>
> >
> > > @@ -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;
> >
> > I do not see the reason for this variable, you can as well put the delay
> > in pg_init_delay and use it directly (and set it to zero after using
> > it) ?
> >
>
> I missed resetting pg_init_delay to zero after using it. I have attached the
> corrected patch with this. This variable keeps the code cleaner(avoids taking
> m->lock). Also having only a boolean in struct multipath keeps it a bit
> smaller.
Ok. I am fine with your justification.
>
> off-topic:
> I think struct multipath can be shrunk even further by making various flags
> like pg_init_required, pg_init_in_progress, queue_io, queue_if_no_path,
> saved_queue_if_no_path in to a single variable. Thoughts?
As Konrad mentioned, it is worth the cost of readability ?
<snip>
> 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@suse.de>
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03-02-2009, 09:48 AM
Nikanth Karthikesan
dm mpath: delay retry activate_path on SCSI_DH_RETRY
On Saturday 21 February 2009 02:41:33 Chandra Seetharaman wrote:
> On Fri, 2009-02-20 at 10:33 +0530, Nikanth Karthikesan wrote:
> > On Friday 20 February 2009 06:15:29 Chandra Seetharaman wrote:
> > > On Thu, 2009-02-19 at 12:40 +0530, Nikanth Karthikesan wrote:
> > >
> > > <snip>
> > >
> > > > @@ -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;
> > >
> > > I do not see the reason for this variable, you can as well put the
> > > delay in pg_init_delay and use it directly (and set it to zero after
> > > using it) ?
> >
> > I missed resetting pg_init_delay to zero after using it. I have attached
> > the corrected patch with this. This variable keeps the code
> > cleaner(avoids taking m->lock). Also having only a boolean in struct
> > multipath keeps it a bit smaller.
>
> Ok. I am fine with your justification.
>
> > off-topic:
> > I think struct multipath can be shrunk even further by making various
> > flags like pg_init_required, pg_init_in_progress, queue_io,
> > queue_if_no_path, saved_queue_if_no_path in to a single variable.
> > Thoughts?
>
> As Konrad mentioned, it is worth the cost of readability ?
>
>
> <snip>
>
> > 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@suse.de>
>
> Acked-by: Chandra Seetharaman <sekharan@us.ibm.com>
>
dm mpath: delay retry activate_path on SCSI_DH_RETRY
