Hi James,
The following patches export busy-status of SCSI LLD to request-based
dm-multipath for proper I/O scheduling.
The patches are created on the following commit of scsi-post-merge-2.6.
---------------------------------------------------------------
commit 454f40af9f0d4cda1c89e1fc0028d5235b150bc7
Author: Mike Christie <[email protected]>
Date: Wed Sep 24 11:46:15 2008 -0500
libiscsi: fix locking in iscsi_eh_device_reset
---------------------------------------------------------------
The changes from the previous version (*) is to check the busy state
everytime instead of using a cached flag inside scsi.
Summary of the patches:
1/2: scsi: refactor sdev/starget/shost busy checking
2/2: scsi: export busy state via q->lld_busy_fn()
Please review and apply.
Thanks,
Kiyoshi Ueda
This patch refactors the busy checking codes of scsi_device,
Scsi_Host and scsi_target. There should be no functional change.
This is a preparation for another patch which exports scsi's busy
state to the block layer for request stacking drivers.
Signed-off-by: Kiyoshi Ueda <[email protected]>
Signed-off-by: Jun'ichi Nomura <[email protected]>
Cc: James Bottomley <[email protected]>
---
drivers/scsi/scsi_lib.c | 30 ++++++++++++++++++++----------
1 files changed, 20 insertions(+), 10 deletions(-)
Index: scsi-post-merge-2.6/drivers/scsi/scsi_lib.c
===================================================================
--- scsi-post-merge-2.6.orig/drivers/scsi/scsi_lib.c
+++ scsi-post-merge-2.6/drivers/scsi/scsi_lib.c
@@ -529,6 +529,14 @@ static void scsi_single_lun_run(struct s
spin_unlock_irqrestore(shost->host_lock, flags);
}
+static inline int scsi_device_is_busy(struct scsi_device *sdev)
+{
+ if (sdev->device_busy >= sdev->queue_depth || sdev->device_blocked)
+ return 1;
+
+ return 0;
+}
+
static inline int scsi_target_is_busy(struct scsi_target *starget)
{
return ((starget->can_queue > 0 &&
@@ -536,6 +544,15 @@ static inline int scsi_target_is_busy(st
starget->target_blocked);
}
+static inline int scsi_host_is_busy(struct Scsi_Host *shost)
+{
+ if ((shost->can_queue > 0 && shost->host_busy >= shost->can_queue) ||
+ shost->host_blocked || shost->host_self_blocked)
+ return 1;
+
+ return 0;
+}
+
/*
* Function: scsi_run_queue()
*
@@ -558,11 +575,7 @@ static void scsi_run_queue(struct reques
scsi_single_lun_run(sdev);
spin_lock_irqsave(shost->host_lock, flags);
- while (!list_empty(&shost->starved_list) &&
- !shost->host_blocked && !shost->host_self_blocked &&
- !((shost->can_queue > 0) &&
- (shost->host_busy >= shost->can_queue))) {
-
+ while (!list_empty(&shost->starved_list) && !scsi_host_is_busy(shost)) {
int flagset;
/*
@@ -1348,8 +1361,6 @@ int scsi_prep_fn(struct request_queue *q
static inline int scsi_dev_queue_ready(struct request_queue *q,
struct scsi_device *sdev)
{
- if (sdev->device_busy >= sdev->queue_depth)
- return 0;
if (sdev->device_busy == 0 && sdev->device_blocked) {
/*
* unblock after device_blocked iterates to zero
@@ -1363,7 +1374,7 @@ static inline int scsi_dev_queue_ready(s
return 0;
}
}
- if (sdev->device_blocked)
+ if (scsi_device_is_busy(sdev))
return 0;
return 1;
@@ -1440,8 +1451,7 @@ static inline int scsi_host_queue_ready(
return 0;
}
}
- if ((shost->can_queue > 0 && shost->host_busy >= shost->can_queue) ||
- shost->host_blocked || shost->host_self_blocked) {
+ if (scsi_host_is_busy(shost)) {
if (list_empty(&sdev->starved_entry))
list_add_tail(&sdev->starved_entry, &shost->starved_list);
return 0;
This patch implements q->lld_busy_fn() for scsi mid layer to export
its busy state for request stacking drivers.
For efficiency, no lock is taken to check the busy state of
shost/starget/sdev, since the returned value is not guaranteed and
may be changed after request stacking drivers call the function,
regardless of taking lock or not.
When scsi can't dispatch I/Os anymore and needs to kill I/Os
(e.g. !sdev), scsi needs to return 'not busy'.
Otherwise, request stacking drivers may hold requests forever.
Signed-off-by: Kiyoshi Ueda <[email protected]>
Signed-off-by: Jun'ichi Nomura <[email protected]>
Cc: James Bottomley <[email protected]>
---
drivers/scsi/scsi_lib.c | 32 ++++++++++++++++++++++++++++++++
1 files changed, 32 insertions(+)
Index: scsi-post-merge-2.6/drivers/scsi/scsi_lib.c
===================================================================
--- scsi-post-merge-2.6.orig/drivers/scsi/scsi_lib.c
+++ scsi-post-merge-2.6/drivers/scsi/scsi_lib.c
@@ -1465,6 +1465,37 @@ static inline int scsi_host_queue_ready(
}
/*
+ * Busy state exporting function for request stacking drivers.
+ *
+ * For efficiency, no lock is taken to check the busy state of
+ * shost/starget/sdev, since the returned value is not guaranteed and
+ * may be changed after request stacking drivers call the function,
+ * regardless of taking lock or not.
+ *
+ * When scsi can't dispatch I/Os anymore and needs to kill I/Os
+ * (e.g. !sdev), scsi needs to return 'not busy'.
+ * Otherwise, request stacking drivers may hold requests forever.
+ */
+static int scsi_lld_busy(struct request_queue *q)
+{
+ struct scsi_device *sdev = q->queuedata;
+ struct Scsi_Host *shost;
+ struct scsi_target *starget;
+
+ if (!sdev)
+ return 0;
+
+ shost = sdev->host;
+ starget = scsi_target(sdev);
+
+ if (scsi_host_in_recovery(shost) || scsi_host_is_busy(shost) ||
+ scsi_target_is_busy(starget) || scsi_device_is_busy(sdev))
+ return 1;
+
+ return 0;
+}
+
+/*
* Kill a request for a dead device
*/
static void scsi_kill_request(struct request *req, struct request_queue *q)
@@ -1767,6 +1798,7 @@ struct request_queue *scsi_alloc_queue(s
blk_queue_prep_rq(q, scsi_prep_fn);
blk_queue_softirq_done(q, scsi_softirq_done);
blk_queue_rq_timed_out(q, scsi_times_out);
+ blk_queue_lld_busy(q, scsi_lld_busy);
return q;
}