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Date:	Mon,  2 Nov 2015 12:21:45 +0800
From:	Bob Liu <bob.liu@...cle.com>
To:	xen-devel@...ts.xen.org
Cc:	linux-kernel@...r.kernel.org, roger.pau@...rix.com,
	konrad.wilk@...cle.com, felipe.franciosi@...rix.com, axboe@...com,
	avanzini.arianna@...il.com, rafal.mielniczuk@...rix.com,
	jonathan.davies@...rix.com, david.vrabel@...rix.com,
	Bob Liu <bob.liu@...cle.com>
Subject: [PATCH v4 09/10] xen/blkfront: make persistent grants per-queue

Make persistent grants per-queue/ring instead of per-device, so that we can
drop the 'dev_lock' and get better scalability.

Signed-off-by: Bob Liu <bob.liu@...cle.com>
---
 drivers/block/xen-blkfront.c | 89 +++++++++++++++++---------------------------
 1 file changed, 34 insertions(+), 55 deletions(-)

diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
index 23096d7..eb19f08 100644
--- a/drivers/block/xen-blkfront.c
+++ b/drivers/block/xen-blkfront.c
@@ -133,6 +133,8 @@ struct blkfront_ring_info {
 	struct gnttab_free_callback callback;
 	struct blk_shadow shadow[BLK_MAX_RING_SIZE];
 	struct list_head indirect_pages;
+	struct list_head grants;
+	unsigned int persistent_gnts_c;
 	unsigned long shadow_free;
 	struct blkfront_info *dev_info;
 };
@@ -144,8 +146,6 @@ struct blkfront_ring_info {
  */
 struct blkfront_info
 {
-	/* Lock to proect info->grants list shared by multi rings */
-	spinlock_t dev_lock;
 	struct mutex mutex;
 	struct xenbus_device *xbdev;
 	struct gendisk *gd;
@@ -155,8 +155,6 @@ struct blkfront_info
 	/* Number of pages per ring buffer */
 	unsigned int nr_ring_pages;
 	struct request_queue *rq;
-	struct list_head grants;
-	unsigned int persistent_gnts_c;
 	unsigned int feature_flush;
 	unsigned int feature_discard:1;
 	unsigned int feature_secdiscard:1;
@@ -231,7 +229,6 @@ static int fill_grant_buffer(struct blkfront_ring_info *rinfo, int num)
 	struct grant *gnt_list_entry, *n;
 	int i = 0;
 
-	spin_lock_irq(&info->dev_lock);
 	while(i < num) {
 		gnt_list_entry = kzalloc(sizeof(struct grant), GFP_NOIO);
 		if (!gnt_list_entry)
@@ -247,35 +244,32 @@ static int fill_grant_buffer(struct blkfront_ring_info *rinfo, int num)
 		}
 
 		gnt_list_entry->gref = GRANT_INVALID_REF;
-		list_add(&gnt_list_entry->node, &info->grants);
+		list_add(&gnt_list_entry->node, &rinfo->grants);
 		i++;
 	}
-	spin_unlock_irq(&info->dev_lock);
 
 	return 0;
 
 out_of_memory:
 	list_for_each_entry_safe(gnt_list_entry, n,
-	                         &info->grants, node) {
+				 &rinfo->grants, node) {
 		list_del(&gnt_list_entry->node);
 		if (info->feature_persistent)
 			__free_page(pfn_to_page(gnt_list_entry->pfn));
 		kfree(gnt_list_entry);
 		i--;
 	}
-	spin_unlock_irq(&info->dev_lock);
 	BUG_ON(i != 0);
 	return -ENOMEM;
 }
 
 static struct grant *get_grant(grant_ref_t *gref_head,
                                unsigned long pfn,
-                               struct blkfront_info *info)
+			       struct blkfront_ring_info *info)
 {
 	struct grant *gnt_list_entry;
 	unsigned long buffer_gfn;
 
-	spin_lock(&info->dev_lock);
 	BUG_ON(list_empty(&info->grants));
 	gnt_list_entry = list_first_entry(&info->grants, struct grant,
 	                                  node);
@@ -283,21 +277,19 @@ static struct grant *get_grant(grant_ref_t *gref_head,
 
 	if (gnt_list_entry->gref != GRANT_INVALID_REF) {
 		info->persistent_gnts_c--;
-		spin_unlock(&info->dev_lock);
 		return gnt_list_entry;
 	}
-	spin_unlock(&info->dev_lock);
 
 	/* Assign a gref to this page */
 	gnt_list_entry->gref = gnttab_claim_grant_reference(gref_head);
 	BUG_ON(gnt_list_entry->gref == -ENOSPC);
-	if (!info->feature_persistent) {
+	if (!info->dev_info->feature_persistent) {
 		BUG_ON(!pfn);
 		gnt_list_entry->pfn = pfn;
 	}
 	buffer_gfn = pfn_to_gfn(gnt_list_entry->pfn);
 	gnttab_grant_foreign_access_ref(gnt_list_entry->gref,
-	                                info->xbdev->otherend_id,
+					info->dev_info->xbdev->otherend_id,
 	                                buffer_gfn, 0);
 	return gnt_list_entry;
 }
@@ -559,13 +551,13 @@ static int blkif_queue_request(struct request *req, struct blkfront_ring_info *r
 					list_del(&indirect_page->lru);
 					pfn = page_to_pfn(indirect_page);
 				}
-				gnt_list_entry = get_grant(&gref_head, pfn, info);
+				gnt_list_entry = get_grant(&gref_head, pfn, rinfo);
 				rinfo->shadow[id].indirect_grants[n] = gnt_list_entry;
 				segments = kmap_atomic(pfn_to_page(gnt_list_entry->pfn));
 				ring_req->u.indirect.indirect_grefs[n] = gnt_list_entry->gref;
 			}
 
-			gnt_list_entry = get_grant(&gref_head, page_to_pfn(sg_page(sg)), info);
+			gnt_list_entry = get_grant(&gref_head, page_to_pfn(sg_page(sg)), rinfo);
 			ref = gnt_list_entry->gref;
 
 			rinfo->shadow[id].grants_used[i] = gnt_list_entry;
@@ -992,7 +984,7 @@ static void blkif_restart_queue(struct work_struct *work)
 
 static void blkif_free_ring(struct blkfront_ring_info *rinfo)
 {
-	struct grant *persistent_gnt;
+	struct grant *persistent_gnt, *n;
 	struct blkfront_info *info = rinfo->dev_info;
 	int i, j, segs;
 
@@ -1010,6 +1002,23 @@ static void blkif_free_ring(struct blkfront_ring_info *rinfo)
 		}
 	}
 
+	/* Remove all persistent grants */
+	if (!list_empty(&rinfo->grants)) {
+		list_for_each_entry_safe(persistent_gnt, n,
+					 &rinfo->grants, node) {
+			list_del(&persistent_gnt->node);
+			if (persistent_gnt->gref != GRANT_INVALID_REF) {
+				gnttab_end_foreign_access(persistent_gnt->gref,
+							  0, 0UL);
+				rinfo->persistent_gnts_c--;
+			}
+			if (info->feature_persistent)
+				__free_page(pfn_to_page(persistent_gnt->pfn));
+			kfree(persistent_gnt);
+		}
+	}
+	BUG_ON(rinfo->persistent_gnts_c != 0);
+
 	for (i = 0; i < BLK_RING_SIZE(info); i++) {
 		/*
 		 * Clear persistent grants present in requests already
@@ -1075,37 +1084,17 @@ free_shadow:
 
 static void blkif_free(struct blkfront_info *info, int suspend)
 {
-	struct grant *persistent_gnt, *n;
 	int i;
 
 	/* Prevent new requests being issued until we fix things up. */
-	spin_lock_irq(&info->dev_lock);
 	info->connected = suspend ?
 		BLKIF_STATE_SUSPENDED : BLKIF_STATE_DISCONNECTED;
 	/* No more blkif_request(). */
 	if (info->rq)
 		blk_mq_stop_hw_queues(info->rq);
 
-	/* Remove all persistent grants */
-	if (!list_empty(&info->grants)) {
-		list_for_each_entry_safe(persistent_gnt, n,
-					 &info->grants, node) {
-			list_del(&persistent_gnt->node);
-			if (persistent_gnt->gref != GRANT_INVALID_REF) {
-				gnttab_end_foreign_access(persistent_gnt->gref,
-							  0, 0UL);
-				info->persistent_gnts_c--;
-			}
-			if (info->feature_persistent)
-				__free_page(pfn_to_page(persistent_gnt->pfn));
-			kfree(persistent_gnt);
-		}
-	}
-	BUG_ON(info->persistent_gnts_c != 0);
-
 	for (i = 0; i < info->nr_rings; i++)
 		blkif_free_ring(&info->rinfo[i]);
-	spin_unlock_irq(&info->dev_lock);
 }
 
 static void blkif_completion(struct blk_shadow *s, struct blkfront_ring_info *rinfo,
@@ -1117,7 +1106,6 @@ static void blkif_completion(struct blk_shadow *s, struct blkfront_ring_info *ri
 	void *shared_data;
 	int nseg;
 	struct blkfront_info *info = rinfo->dev_info;
-	unsigned long flags;
 
 	nseg = s->req.operation == BLKIF_OP_INDIRECT ?
 		s->req.u.indirect.nr_segments : s->req.u.rw.nr_segments;
@@ -1148,10 +1136,8 @@ static void blkif_completion(struct blk_shadow *s, struct blkfront_ring_info *ri
 			if (!info->feature_persistent)
 				pr_alert_ratelimited("backed has not unmapped grant: %u\n",
 						     s->grants_used[i]->gref);
-			spin_lock_irqsave(&info->dev_lock, flags);
-			list_add(&s->grants_used[i]->node, &info->grants);
-			info->persistent_gnts_c++;
-			spin_unlock_irqrestore(&info->dev_lock, flags);
+			list_add(&s->grants_used[i]->node, &rinfo->grants);
+			rinfo->persistent_gnts_c++;
 		} else {
 			/*
 			 * If the grant is not mapped by the backend we end the
@@ -1161,9 +1147,7 @@ static void blkif_completion(struct blk_shadow *s, struct blkfront_ring_info *ri
 			 */
 			gnttab_end_foreign_access(s->grants_used[i]->gref, 0, 0UL);
 			s->grants_used[i]->gref = GRANT_INVALID_REF;
-			spin_lock_irqsave(&info->dev_lock, flags);
-			list_add_tail(&s->grants_used[i]->node, &info->grants);
-			spin_unlock_irqrestore(&info->dev_lock, flags);
+			list_add_tail(&s->grants_used[i]->node, &rinfo->grants);
 		}
 	}
 	if (s->req.operation == BLKIF_OP_INDIRECT) {
@@ -1172,10 +1156,8 @@ static void blkif_completion(struct blk_shadow *s, struct blkfront_ring_info *ri
 				if (!info->feature_persistent)
 					pr_alert_ratelimited("backed has not unmapped grant: %u\n",
 							     s->indirect_grants[i]->gref);
-				spin_lock_irqsave(&info->dev_lock, flags);
-				list_add(&s->indirect_grants[i]->node, &info->grants);
-				info->persistent_gnts_c++;
-				spin_unlock_irqrestore(&info->dev_lock, flags);
+				list_add(&s->indirect_grants[i]->node, &rinfo->grants);
+				rinfo->persistent_gnts_c++;
 			} else {
 				struct page *indirect_page;
 
@@ -1184,14 +1166,12 @@ static void blkif_completion(struct blk_shadow *s, struct blkfront_ring_info *ri
 				 * Add the used indirect page back to the list of
 				 * available pages for indirect grefs.
 				 */
-				spin_lock_irqsave(&info->dev_lock, flags);
 				if (!info->feature_persistent) {
 					indirect_page = pfn_to_page(s->indirect_grants[i]->pfn);
 					list_add(&indirect_page->lru, &rinfo->indirect_pages);
 				}
 				s->indirect_grants[i]->gref = GRANT_INVALID_REF;
-				list_add_tail(&s->indirect_grants[i]->node, &info->grants);
-				spin_unlock_irqrestore(&info->dev_lock, flags);
+				list_add_tail(&s->indirect_grants[i]->node, &rinfo->grants);
 			}
 		}
 	}
@@ -1587,10 +1567,8 @@ static int blkfront_probe(struct xenbus_device *dev,
 	}
 
 	mutex_init(&info->mutex);
-	spin_lock_init(&info->dev_lock);
 	info->xbdev = dev;
 	info->vdevice = vdevice;
-	INIT_LIST_HEAD(&info->grants);
 	info->connected = BLKIF_STATE_DISCONNECTED;
 
 	/* Check if backend supports multiple queues */
@@ -1616,6 +1594,7 @@ static int blkfront_probe(struct xenbus_device *dev,
 		struct blkfront_ring_info *rinfo;
 
 		rinfo = &info->rinfo[r_index];
+		INIT_LIST_HEAD(&rinfo->grants);
 		INIT_LIST_HEAD(&rinfo->indirect_pages);
 		rinfo->dev_info = info;
 		INIT_WORK(&rinfo->work, blkif_restart_queue);
-- 
1.8.3.1

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