[PATCH] scsi_dh_alua: Add module parameter to allow failover to non preferred path without STPG

[PATCH] scsi_dh_alua: Add module parameter to allow failover to non preferred path without STPG

[Stewart, Sean]

Currently ALUA device handler sends STPG command during failover and failback.
Failover can be optimized by implicit failover (by not to sending STPG command),
when 1 is passed as hwhandler parameter in multipath.conf. ex "2 alua 1". We may
need to pass the parameter through module param for alua device handler to optimize
failover if incase retain_attached_hwhandler set in multipath.conf and hwhandler
is set with non-tpgs device handler ex: '1 rdac'.

Signed-off-by: Vijay Chauhan <vijay.chauhan@netapp.com>
Signed-off-by: Sean Stewart <Sean.Stewart@netapp.com>

---
--- a/drivers/scsi/device_handler/scsi_dh_alua.c.orig	2013-03-27 12:18:35.000000000 +0530
+++ b/drivers/scsi/device_handler/scsi_dh_alua.c	2013-03-27 13:23:16.000000000 +0530
@@ -710,6 +710,10 @@ static int alua_set_params(struct scsi_d
 	return result;
 }
 
+static uint optimize_stpg;
+module_param(optimize_stpg, uint, S_IRUGO|S_IWUSR);
+MODULE_PARM_DESC(optimize_stpg, "Send STPG command for Failover on non-preferred path(0=Yes,1=No). Default is 0.");
+
 /*
  * alua_activate - activate a path
  * @sdev: device on the path to be activated
@@ -731,6 +735,9 @@ static int alua_activate(struct scsi_dev
 	if (err != SCSI_DH_OK)
 		goto out;
 
+	if (optimize_stpg)
+		h->flags |= ALUA_OPTIMIZE_STPG;
+
 	if (h->tpgs & TPGS_MODE_EXPLICIT) {
 		switch (h->state) {
 		case TPGS_STATE_NONOPTIMIZED:
--

Re: [PATCH] scsi_dh_alua: Add module parameter to allow failover to non preferred path without STPG

[Hannes Reinecke]

On 03/28/2013 11:07 PM, Stewart, Sean wrote:
> Currently ALUA device handler sends STPG command during failover and failback.
> Failover can be optimized by implicit failover (by not to sending STPG command),
> when 1 is passed as hwhandler parameter in multipath.conf. ex "2 alua 1". We may
> need to pass the parameter through module param for alua device handler to optimize
> failover if incase retain_attached_hwhandler set in multipath.conf and hwhandler
> is set with non-tpgs device handler ex: '1 rdac'.
>
> Signed-off-by: Vijay Chauhan <vijay.chauhan@netapp.com>
> Signed-off-by: Sean Stewart <Sean.Stewart@netapp.com>
>
Acked-by: Hannes Reinecke <hare@suse.de>

Cheers,

Hannes

Re: [PATCH] scsi_dh_alua: Add module parameter to allow failover to non preferred path without STPG

[Ewan Milne]

On Thu, 2013-03-28 at 22:07 +0000, Stewart, Sean wrote:
> +static uint optimize_stpg;
> +module_param(optimize_stpg, uint, S_IRUGO|S_IWUSR);
> +MODULE_PARM_DESC(optimize_stpg, "Send STPG command for Failover on non-preferred path(0=Yes,1=No). Default is 0.");

Could you possibly reword the description?  When I first read this, it
seemed backwards to have 0=Yes and 1=No.

-Ewan D. Milne <emilne@redhat.com>

RE: [PATCH] scsi_dh_alua: Add module parameter to allow failover to non preferred path without STPG

[Stewart, Sean]

How about the following?  Reworded in a way such that 0 means no and 1 means yes.

+static uint optimize_stpg;
+module_param(optimize_stpg, uint, S_IRUGO|S_IWUSR); 
+MODULE_PARM_DESC(optimize_stpg, "Allow use of a non-optimized path, rather than sending a STPG, when implicit TPGS is supported (0=No,1=Yes). Default is 0.");


Thanks,
Sean Stewart

-----Original Message-----
From: Ewan Milne [mailto:emilne@redhat.com] 
Sent: Monday, April 01, 2013 9:25 AM
To: Stewart, Sean
Cc: linux-scsi@vger.kernel.org; dm-devel@redhat.com; James.Bottomley@suse.de; snitzer@redhat.com; hare@suse.de
Subject: Re: [PATCH] scsi_dh_alua: Add module parameter to allow failover to non preferred path without STPG

On Thu, 2013-03-28 at 22:07 +0000, Stewart, Sean wrote:
> +static uint optimize_stpg;
> +module_param(optimize_stpg, uint, S_IRUGO|S_IWUSR); 
> +MODULE_PARM_DESC(optimize_stpg, "Send STPG command for Failover on 
> +non-preferred path(0=Yes,1=No). Default is 0.");

Could you possibly reword the description?  When I first read this, it seemed backwards to have 0=Yes and 1=No.

-Ewan D. Milne <emilne@redhat.com>

RE: [PATCH] scsi_dh_alua: Add module parameter to allow failover to non preferred path without STPG

[Ewan Milne]

On Mon, 2013-04-01 at 21:18 +0000, Stewart, Sean wrote:
> How about the following?  Reworded in a way such that 0 means no and 1 means yes.
> 
> +static uint optimize_stpg;
> +module_param(optimize_stpg, uint, S_IRUGO|S_IWUSR); 
> +MODULE_PARM_DESC(optimize_stpg, "Allow use of a non-optimized path, rather than sending a STPG, when implicit TPGS is supported (0=No,1=Yes). Default is 0.");

Great, thank you.

-Ewan D. Milne <emilne@redhat.com>