iommu/iova: Extend rbtree node caching

The cached node mechanism provides a significant performance benefit for
allocations using a 32-bit DMA mask, but in the case of non-PCI devices
or where the 32-bit space is full, the loss of this benefit can be
significant - on large systems there can be many thousands of entries in
the tree, such that walking all the way down to find free space every
time becomes increasingly awful.

Maintain a similar cached node for the whole IOVA space as a superset of
the 32-bit space so that performance can remain much more consistent.

Inspired by work by Zhen Lei <thunder.leizhen@huawei.com>.
Tested-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Tested-by: Zhen Lei <thunder.leizhen@huawei.com>
Tested-by: Nate Watterson <nwatters@codeaurora.org>
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>

drivers/iommu/iova.c

@@ -48,6 +48,7 @@ init_iova_domain(struct iova_domain *iovad, unsigned long granule,
 
 	spin_lock_init(&iovad->iova_rbtree_lock);
 	iovad->rbroot = RB_ROOT;
+	iovad->cached_node = NULL;
 	iovad->cached32_node = NULL;
 	iovad->granule = granule;
 	iovad->start_pfn = start_pfn;
@@ -110,48 +111,44 @@ EXPORT_SYMBOL_GPL(init_iova_flush_queue);
 static struct rb_node *
 __get_cached_rbnode(struct iova_domain *iovad, unsigned long *limit_pfn)
 {
-	if ((*limit_pfn > iovad->dma_32bit_pfn) ||
-		(iovad->cached32_node == NULL))
+	struct rb_node *cached_node = NULL;
+	struct iova *curr_iova;
+
+	if (*limit_pfn <= iovad->dma_32bit_pfn)
+		cached_node = iovad->cached32_node;
+	if (!cached_node)
+		cached_node = iovad->cached_node;
+	if (!cached_node)
 		return rb_last(&iovad->rbroot);
-	else {
-		struct rb_node *prev_node = rb_prev(iovad->cached32_node);
-		struct iova *curr_iova =
-			rb_entry(iovad->cached32_node, struct iova, node);
-		*limit_pfn = curr_iova->pfn_lo;
-		return prev_node;
-	}
+
+	curr_iova = rb_entry(cached_node, struct iova, node);
+	*limit_pfn = min(*limit_pfn, curr_iova->pfn_lo);
+
+	return rb_prev(cached_node);
 }
 
 static void
-__cached_rbnode_insert_update(struct iova_domain *iovad,
-	unsigned long limit_pfn, struct iova *new)
+__cached_rbnode_insert_update(struct iova_domain *iovad, struct iova *new)
 {
-	if (limit_pfn != iovad->dma_32bit_pfn)
-		return;
-	iovad->cached32_node = &new->node;
+	if (new->pfn_hi < iovad->dma_32bit_pfn)
+		iovad->cached32_node = &new->node;
+	else
+		iovad->cached_node = &new->node;
 }
 
 static void
 __cached_rbnode_delete_update(struct iova_domain *iovad, struct iova *free)
 {
 	struct iova *cached_iova;
-	struct rb_node *curr;
 
-	if (!iovad->cached32_node)
-		return;
-	curr = iovad->cached32_node;
-	cached_iova = rb_entry(curr, struct iova, node);
+	cached_iova = rb_entry(iovad->cached32_node, struct iova, node);
+	if (free->pfn_hi < iovad->dma_32bit_pfn &&
+	    iovad->cached32_node && free->pfn_lo >= cached_iova->pfn_lo)
+		iovad->cached32_node = rb_next(&free->node);
 
-	if (free->pfn_lo >= cached_iova->pfn_lo) {
-		struct rb_node *node = rb_next(&free->node);
-		struct iova *iova = rb_entry(node, struct iova, node);
-
-		/* only cache if it's below 32bit pfn */
-		if (node && iova->pfn_lo < iovad->dma_32bit_pfn)
-			iovad->cached32_node = node;
-		else
-			iovad->cached32_node = NULL;
-	}
+	cached_iova = rb_entry(iovad->cached_node, struct iova, node);
+	if (iovad->cached_node && free->pfn_lo >= cached_iova->pfn_lo)
+		iovad->cached_node = rb_next(&free->node);
 }
 
 /* Insert the iova into domain rbtree by holding writer lock */
@@ -188,7 +185,7 @@ static int __alloc_and_insert_iova_range(struct iova_domain *iovad,
 {
 	struct rb_node *prev, *curr = NULL;
 	unsigned long flags;
-	unsigned long saved_pfn, new_pfn;
+	unsigned long new_pfn;
 	unsigned long align_mask = ~0UL;
 
 	if (size_aligned)
@@ -196,7 +193,6 @@ static int __alloc_and_insert_iova_range(struct iova_domain *iovad,
 
 	/* Walk the tree backwards */
 	spin_lock_irqsave(&iovad->iova_rbtree_lock, flags);
-	saved_pfn = limit_pfn;
 	curr = __get_cached_rbnode(iovad, &limit_pfn);
 	prev = curr;
 	while (curr) {
@@ -226,7 +222,7 @@ static int __alloc_and_insert_iova_range(struct iova_domain *iovad,
 
 	/* If we have 'prev', it's a valid place to start the insertion. */
 	iova_insert_rbtree(&iovad->rbroot, new, prev);
-	__cached_rbnode_insert_update(iovad, saved_pfn, new);
+	__cached_rbnode_insert_update(iovad, new);
 
 	spin_unlock_irqrestore(&iovad->iova_rbtree_lock, flags);
 

include/linux/iova.h

@@ -70,7 +70,8 @@ struct iova_fq {
 struct iova_domain {
 	spinlock_t	iova_rbtree_lock; /* Lock to protect update of rbtree */
 	struct rb_root	rbroot;		/* iova domain rbtree root */
-	struct rb_node	*cached32_node; /* Save last alloced node */
+	struct rb_node	*cached_node;	/* Save last alloced node */
+	struct rb_node	*cached32_node; /* Save last 32-bit alloced node */
 	unsigned long	granule;	/* pfn granularity for this domain */
 	unsigned long	start_pfn;	/* Lower limit for this domain */
 	unsigned long	dma_32bit_pfn;