Attachment 314162 Details for Bug 438761 – Add a workqueue to handle events

Add a workqueue to handle events

07-add-workqueue (text/plain), 4.07 KB, created by IBM Bug Proxy on 2008-08-13 00:51:43 UTC

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Creator: IBM Bug Proxy

Created: 2008-08-13 00:51:43 UTC

Size: 4.07 KB

patch

obsolete

>Subject: scsi_dh: Add a single threaded workqueue for initializing paths
>
>From: Chandra Seetharaman <sekharan@us.ibm.com>
>
>Before this patch set (SCSI hardware handlers), initialization of a
>path was done asynchronously. Doing that requires a workqueue in each 
>device/hardware handler module and leads to unneccessary complication
>in the device handler code, making it difficult to read the code and
>follow the state diagram.
>
>Moving that workqueue to this level makes the device handler code simpler.
>Hence, the workqueue is moved to dm level.
>
>A new workqueue is added instead of adding it to the existing workqueue
>(kmpathd) for the following reasons:
>	1. Device activation has to happen faster, stacking them along
>	   with the other workqueue might lead to unnecessary delay
>	   in the activation of the path.
>	2. The effect could be felt the other way too. i.e the current
>	   events that are handled by the existing workqueue might get
>	   a delayed response.
>
>Signed-off-by: Chandra Seetharaman <sekharan@us.ibm.com>
>---
>Index: linux-2.6.18.ppc64/drivers/md/dm-mpath.c
>===================================================================
>--- linux-2.6.18.ppc64.orig/drivers/md/dm-mpath.c
>+++ linux-2.6.18.ppc64/drivers/md/dm-mpath.c
>@@ -86,6 +86,7 @@ struct multipath {
> 	unsigned queue_size;
> 
> 	struct work_struct trigger_event;
>+	struct work_struct activate_path;
> 
> 	/*
> 	 * We must use a mempool of mpath_io structs so that we
>@@ -108,11 +109,10 @@ typedef int (*action_fn) (struct pgpath 
> 
> static kmem_cache_t *_mpio_cache;
> 
>-struct workqueue_struct *kmultipathd;
>+struct workqueue_struct *kmultipathd, *kmpath_handlerd;
> static void process_queued_ios(void *data);
> static void trigger_event(void *data);
>-static void pg_init_done(struct path *, int);
>-
>+static void activate_path(void *data);
> 
> /*-----------------------------------------------
>  * Allocation routines
>@@ -189,6 +189,7 @@ static struct multipath *alloc_multipath
> 		m->queue_io = 1;
> 		INIT_WORK(&m->process_queued_ios, process_queued_ios, m);
> 		INIT_WORK(&m->trigger_event, trigger_event, m);
>+		INIT_WORK(&m->activate_path, activate_path, m);
> 		m->mpio_pool = mempool_create_slab_pool(MIN_IOS, _mpio_cache);
> 		if (!m->mpio_pool) {
> 			kfree(m);
>@@ -443,12 +444,8 @@ out:
> 		if (hwh->type)
> 			hwh->type->pg_init(hwh, pgpath->pg->bypassed,
> 							 &pgpath->path);
>-		else {
>-			int ret;
>-			struct path *path = &pgpath->path;
>-			ret = scsi_dh_activate(bdev_get_queue(path->dev->bdev));
>-			pg_init_done(path, ret);
>-		}
>+		else
>+			queue_work(kmpath_handlerd, &m->activate_path);
> 	}
> 
> 	if (!must_queue)
>@@ -845,6 +842,7 @@ static void multipath_dtr(struct dm_targ
> {
> 	struct multipath *m = (struct multipath *) ti->private;
> 
>+	flush_workqueue(kmpath_handlerd);
> 	flush_workqueue(kmultipathd);
> 	free_multipath(m);
> }
>@@ -1165,6 +1163,16 @@ static void pg_init_done(struct path *pa
> 	spin_unlock_irqrestore(&m->lock, flags);
> }
> 
>+static void activate_path(void *data)
>+{
>+	int ret;
>+	struct multipath *m = (struct multipath *) data;
>+	struct path *path = &m->current_pgpath->path;
>+
>+	ret = scsi_dh_activate(bdev_get_queue(path->dev->bdev));
>+	pg_init_done(path, ret);
>+}
>+
> /*
>  * end_io handling
>  */
>@@ -1529,6 +1537,21 @@ static int __init dm_multipath_init(void
> 		return -ENOMEM;
> 	}
> 
>+	/*
>+	 * A separate workqueue is used to handle the device handlers
>+	 * to avoid overloading existing workqueue. Overloading the
>+	 * old workqueue would also create a bottleneck in the
>+	 * path of the storage hardware device activation.
>+	 */
>+	kmpath_handlerd = create_singlethread_workqueue("kmpath_handlerd");
>+	if (!kmpath_handlerd) {
>+		DMERR("failed to create workqueue kmpath_handlerd");
>+		destroy_workqueue(kmultipathd);
>+		dm_unregister_target(&multipath_target);
>+		kmem_cache_destroy(_mpio_cache);
>+		return -ENOMEM;
>+	}
>+
> 	DMINFO("version %u.%u.%u loaded",
> 	       multipath_target.version[0], multipath_target.version[1],
> 	       multipath_target.version[2]);
>@@ -1540,6 +1563,7 @@ static void __exit dm_multipath_exit(voi
> {
> 	int r;
> 
>+	destroy_workqueue(kmpath_handlerd);
> 	destroy_workqueue(kmultipathd);
> 
> 	r = dm_unregister_target(&multipath_target);

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