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Subject[PATCH v5 3/6] iommu/iova: Extend rbtree node caching
Date
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>
---

v5: Fixed __cached_rbnode_delete_update() logic to update both nodes
when necessary

drivers/iommu/iova.c | 60 ++++++++++++++++++++++++----------------------------
include/linux/iova.h | 3 ++-
2 files changed, 30 insertions(+), 33 deletions(-)

diff --git a/drivers/iommu/iova.c b/drivers/iommu/iova.c
index 20be9a8b3188..c6f5a22f8d20 100644
--- a/drivers/iommu/iova.c
+++ b/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);

diff --git a/include/linux/iova.h b/include/linux/iova.h
index d179b9bf7814..69ea3e258ff2 100644
--- a/include/linux/iova.h
+++ b/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;
--
2.13.4.dirty
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