xen-blkback: make the queue of free requests per backend

Remove the last dependency from blkbk by moving the list of free
requests to blkif. This change reduces the contention on the list of
available requests.

Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: xen-devel@lists.xen.org
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

drivers/block/xen-blkback/blkback.c

@@ -49,20 +49,6 @@
 #include <xen/balloon.h>
 #include "common.h"
 
-/*
- * These are rather arbitrary. They are fairly large because adjacent requests
- * pulled from a communication ring are quite likely to end up being part of
- * the same scatter/gather request at the disc.
- *
- * ** TRY INCREASING 'xen_blkif_reqs' IF WRITE SPEEDS SEEM TOO LOW **
- *
- * This will increase the chances of being able to write whole tracks.
- * 64 should be enough to keep us competitive with Linux.
- */
-static int xen_blkif_reqs = 64;
-module_param_named(reqs, xen_blkif_reqs, int, 0);
-MODULE_PARM_DESC(reqs, "Number of blkback requests to allocate");
-
 /*
  * Maximum number of unused free pages to keep in the internal buffer.
  * Setting this to a value too low will reduce memory used in each backend,
@@ -112,53 +98,11 @@ MODULE_PARM_DESC(max_persistent_grants,
 static unsigned int log_stats;
 module_param(log_stats, int, 0644);
 
-/*
- * Each outstanding request that we've passed to the lower device layers has a
- * 'pending_req' allocated to it. Each buffer_head that completes decrements
- * the pendcnt towards zero. When it hits zero, the specified domain has a
- * response queued for it, with the saved 'id' passed back.
- */
-struct pending_req {
-	struct xen_blkif	*blkif;
-	u64			id;
-	int			nr_pages;
-	atomic_t		pendcnt;
-	unsigned short		operation;
-	int			status;
-	struct list_head	free_list;
-	struct page		*pages[BLKIF_MAX_SEGMENTS_PER_REQUEST];
-	struct persistent_gnt	*persistent_gnts[BLKIF_MAX_SEGMENTS_PER_REQUEST];
-	grant_handle_t		grant_handles[BLKIF_MAX_SEGMENTS_PER_REQUEST];
-};
-
 #define BLKBACK_INVALID_HANDLE (~0)
 
 /* Number of free pages to remove on each call to free_xenballooned_pages */
 #define NUM_BATCH_FREE_PAGES 10
 
-struct xen_blkbk {
-	struct pending_req	*pending_reqs;
-	/* List of all 'pending_req' available */
-	struct list_head	pending_free;
-	/* And its spinlock. */
-	spinlock_t		pending_free_lock;
-	wait_queue_head_t	pending_free_wq;
-};
-
-static struct xen_blkbk *blkbk;
-
-/*
- * Little helpful macro to figure out the index and virtual address of the
- * pending_pages[..]. For each 'pending_req' we have have up to
- * BLKIF_MAX_SEGMENTS_PER_REQUEST (11) pages. The seg would be from 0 through
- * 10 and would index in the pending_pages[..].
- */
-static inline int vaddr_pagenr(struct pending_req *req, int seg)
-{
-	return (req - blkbk->pending_reqs) *
-		BLKIF_MAX_SEGMENTS_PER_REQUEST + seg;
-}
-
 static inline int get_free_page(struct xen_blkif *blkif, struct page **page)
 {
 	unsigned long flags;
@@ -485,18 +429,18 @@ finished:
 /*
  * Retrieve from the 'pending_reqs' a free pending_req structure to be used.
  */
-static struct pending_req *alloc_req(void)
+static struct pending_req *alloc_req(struct xen_blkif *blkif)
 {
 	struct pending_req *req = NULL;
 	unsigned long flags;
 
-	spin_lock_irqsave(&blkbk->pending_free_lock, flags);
-	if (!list_empty(&blkbk->pending_free)) {
-		req = list_entry(blkbk->pending_free.next, struct pending_req,
+	spin_lock_irqsave(&blkif->pending_free_lock, flags);
+	if (!list_empty(&blkif->pending_free)) {
+		req = list_entry(blkif->pending_free.next, struct pending_req,
 				 free_list);
 		list_del(&req->free_list);
 	}
-	spin_unlock_irqrestore(&blkbk->pending_free_lock, flags);
+	spin_unlock_irqrestore(&blkif->pending_free_lock, flags);
 	return req;
 }
 
@@ -504,17 +448,17 @@ static struct pending_req *alloc_req(void)
  * Return the 'pending_req' structure back to the freepool. We also
  * wake up the thread if it was waiting for a free page.
  */
-static void free_req(struct pending_req *req)
+static void free_req(struct xen_blkif *blkif, struct pending_req *req)
 {
 	unsigned long flags;
 	int was_empty;
 
-	spin_lock_irqsave(&blkbk->pending_free_lock, flags);
-	was_empty = list_empty(&blkbk->pending_free);
-	list_add(&req->free_list, &blkbk->pending_free);
-	spin_unlock_irqrestore(&blkbk->pending_free_lock, flags);
+	spin_lock_irqsave(&blkif->pending_free_lock, flags);
+	was_empty = list_empty(&blkif->pending_free);
+	list_add(&req->free_list, &blkif->pending_free);
+	spin_unlock_irqrestore(&blkif->pending_free_lock, flags);
 	if (was_empty)
-		wake_up(&blkbk->pending_free_wq);
+		wake_up(&blkif->pending_free_wq);
 }
 
 /*
@@ -649,8 +593,8 @@ int xen_blkif_schedule(void *arg)
 		if (timeout == 0)
 			goto purge_gnt_list;
 		timeout = wait_event_interruptible_timeout(
-			blkbk->pending_free_wq,
-			!list_empty(&blkbk->pending_free) ||
+			blkif->pending_free_wq,
+			!list_empty(&blkif->pending_free) ||
 			kthread_should_stop(),
 			timeout);
 		if (timeout == 0)
@@ -907,7 +851,7 @@ static int dispatch_other_io(struct xen_blkif *blkif,
 			     struct blkif_request *req,
 			     struct pending_req *pending_req)
 {
-	free_req(pending_req);
+	free_req(blkif, pending_req);
 	make_response(blkif, req->u.other.id, req->operation,
 		      BLKIF_RSP_EOPNOTSUPP);
 	return -EIO;
@@ -967,7 +911,7 @@ static void __end_block_io_op(struct pending_req *pending_req, int error)
 			if (atomic_read(&pending_req->blkif->drain))
 				complete(&pending_req->blkif->drain_complete);
 		}
-		free_req(pending_req);
+		free_req(pending_req->blkif, pending_req);
 	}
 }
 
@@ -1010,7 +954,7 @@ __do_block_io_op(struct xen_blkif *blkif)
 			break;
 		}
 
-		pending_req = alloc_req();
+		pending_req = alloc_req(blkif);
 		if (NULL == pending_req) {
 			blkif->st_oo_req++;
 			more_to_do = 1;
@@ -1044,7 +988,7 @@ __do_block_io_op(struct xen_blkif *blkif)
 				goto done;
 			break;
 		case BLKIF_OP_DISCARD:
-			free_req(pending_req);
+			free_req(blkif, pending_req);
 			if (dispatch_discard_io(blkif, &req))
 				goto done;
 			break;
@@ -1246,7 +1190,7 @@ static int dispatch_rw_block_io(struct xen_blkif *blkif,
  fail_response:
 	/* Haven't submitted any bio's yet. */
 	make_response(blkif, req->u.rw.id, req->operation, BLKIF_RSP_ERROR);
-	free_req(pending_req);
+	free_req(blkif, pending_req);
 	msleep(1); /* back off a bit */
 	return -EIO;
 
@@ -1303,51 +1247,20 @@ static void make_response(struct xen_blkif *blkif, u64 id,
 
 static int __init xen_blkif_init(void)
 {
-	int i;
 	int rc = 0;
 
 	if (!xen_domain())
 		return -ENODEV;
 
-	blkbk = kzalloc(sizeof(struct xen_blkbk), GFP_KERNEL);
-	if (!blkbk) {
-		pr_alert(DRV_PFX "%s: out of memory!\n", __func__);
-		return -ENOMEM;
-	}
-
-
-	blkbk->pending_reqs          = kzalloc(sizeof(blkbk->pending_reqs[0]) *
-					xen_blkif_reqs, GFP_KERNEL);
-
-	if (!blkbk->pending_reqs) {
-		rc = -ENOMEM;
-		goto out_of_memory;
-	}
-
 	rc = xen_blkif_interface_init();
 	if (rc)
 		goto failed_init;
 
-	INIT_LIST_HEAD(&blkbk->pending_free);
-	spin_lock_init(&blkbk->pending_free_lock);
-	init_waitqueue_head(&blkbk->pending_free_wq);
-
-	for (i = 0; i < xen_blkif_reqs; i++)
-		list_add_tail(&blkbk->pending_reqs[i].free_list,
-			      &blkbk->pending_free);
-
 	rc = xen_blkif_xenbus_init();
 	if (rc)
 		goto failed_init;
 
-	return 0;
-
- out_of_memory:
-	pr_alert(DRV_PFX "%s: out of memory\n", __func__);
  failed_init:
-	kfree(blkbk->pending_reqs);
-	kfree(blkbk);
-	blkbk = NULL;
 	return rc;
 }
 

drivers/block/xen-blkback/common.h

@@ -192,6 +192,9 @@ struct backend_info;
  */
 #define PERSISTENT_GNT_WAS_ACTIVE	1
 
+/* Number of requests that we can fit in a ring */
+#define XEN_BLKIF_REQS			32
+
 struct persistent_gnt {
 	struct page *page;
 	grant_ref_t gnt;
@@ -242,6 +245,14 @@ struct xen_blkif {
 	int			free_pages_num;
 	struct list_head	free_pages;
 
+	/* Allocation of pending_reqs */
+	struct pending_req	*pending_reqs;
+	/* List of all 'pending_req' available */
+	struct list_head	pending_free;
+	/* And its spinlock. */
+	spinlock_t		pending_free_lock;
+	wait_queue_head_t	pending_free_wq;
+
 	/* statistics */
 	unsigned long		st_print;
 	unsigned long long			st_rd_req;
@@ -255,6 +266,25 @@ struct xen_blkif {
 	wait_queue_head_t	waiting_to_free;
 };
 
+/*
+ * Each outstanding request that we've passed to the lower device layers has a
+ * 'pending_req' allocated to it. Each buffer_head that completes decrements
+ * the pendcnt towards zero. When it hits zero, the specified domain has a
+ * response queued for it, with the saved 'id' passed back.
+ */
+struct pending_req {
+	struct xen_blkif	*blkif;
+	u64			id;
+	int			nr_pages;
+	atomic_t		pendcnt;
+	unsigned short		operation;
+	int			status;
+	struct list_head	free_list;
+	struct page		*pages[BLKIF_MAX_SEGMENTS_PER_REQUEST];
+	struct persistent_gnt	*persistent_gnts[BLKIF_MAX_SEGMENTS_PER_REQUEST];
+	grant_handle_t		grant_handles[BLKIF_MAX_SEGMENTS_PER_REQUEST];
+};
+
 
 #define vbd_sz(_v)	((_v)->bdev->bd_part ? \
 			 (_v)->bdev->bd_part->nr_sects : \

drivers/block/xen-blkback/xenbus.c

@@ -105,6 +105,7 @@ static void xen_update_blkif_status(struct xen_blkif *blkif)
 static struct xen_blkif *xen_blkif_alloc(domid_t domid)
 {
 	struct xen_blkif *blkif;
+	int i;
 
 	blkif = kmem_cache_zalloc(xen_blkif_cachep, GFP_KERNEL);
 	if (!blkif)
@@ -124,6 +125,21 @@ static struct xen_blkif *xen_blkif_alloc(domid_t domid)
 	blkif->free_pages_num = 0;
 	atomic_set(&blkif->persistent_gnt_in_use, 0);
 
+	blkif->pending_reqs = kcalloc(XEN_BLKIF_REQS,
+	                              sizeof(blkif->pending_reqs[0]),
+	                              GFP_KERNEL);
+	if (!blkif->pending_reqs) {
+		kmem_cache_free(xen_blkif_cachep, blkif);
+		return ERR_PTR(-ENOMEM);
+	}
+	INIT_LIST_HEAD(&blkif->pending_free);
+	spin_lock_init(&blkif->pending_free_lock);
+	init_waitqueue_head(&blkif->pending_free_wq);
+
+	for (i = 0; i < XEN_BLKIF_REQS; i++)
+		list_add_tail(&blkif->pending_reqs[i].free_list,
+			      &blkif->pending_free);
+
 	return blkif;
 }
 
@@ -203,8 +219,18 @@ static void xen_blkif_disconnect(struct xen_blkif *blkif)
 
 static void xen_blkif_free(struct xen_blkif *blkif)
 {
+	struct pending_req *req;
+	int i = 0;
+
 	if (!atomic_dec_and_test(&blkif->refcnt))
 		BUG();
+
+	/* Check that there is no request in use */
+	list_for_each_entry(req, &blkif->pending_free, free_list)
+		i++;
+	BUG_ON(i != XEN_BLKIF_REQS);
+
+	kfree(blkif->pending_reqs);
 	kmem_cache_free(xen_blkif_cachep, blkif);
 }