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SubjectRe: [PATCH] iommu/iova: Improve alloc_iova performance
Adding Robin.

Robin, can you please have a look?

On Wed, Sep 20, 2017 at 11:28:19AM -0400, David Woods wrote:
> When allocating pages with alloc_iova() where limit_pfn > dma_32bit_pfn
> __alloc_and_insert_iova_range does a linear traversal of the tree to
> find a free block. In the worst case it makes the alloc O(n) for each
> page, where n is the number of pages allocated so far. The worst case
> turns out to be common for drivers that allocate lots of pages at start
> up and never free them.
>
> There is an optimization for allocating 32-bit addresses where it
> starts the search at the point where the previous allocated page was
> inserted. This is sensible, since otherwise it would have to always
> search through all the 64-bit pages first.
>
> To improve this situation, extend the optimization to also keep track
> of the point were the previous 64-bit page was inserted. With this
> change, the search for an available slot can normally be done in
> constant time and the whole alloc_iova only costs O(log n) due to the
> rb tree insert.
>
> Reviewed-by: Chris Metcalf <cmetcalf@mellanox.com>
> Signed-off-by: David Woods <dwoods@mellanox.com>
> ---
> drivers/iommu/iova.c | 82 +++++++++++++++++++++++++++++++++++-----------------
> include/linux/iova.h | 1 +
> 2 files changed, 56 insertions(+), 27 deletions(-)
>
> diff --git a/drivers/iommu/iova.c b/drivers/iommu/iova.c
> index 33edfa7..3c82694 100644
> --- a/drivers/iommu/iova.c
> +++ b/drivers/iommu/iova.c
> @@ -108,15 +108,26 @@ int init_iova_flush_queue(struct iova_domain *iovad,
> EXPORT_SYMBOL_GPL(init_iova_flush_queue);
>
> static struct rb_node *
> -__get_cached_rbnode(struct iova_domain *iovad, unsigned long *limit_pfn)
> +__get_cached_rbnode(struct iova_domain *iovad, unsigned long limit_pfn)
> {
> - if ((*limit_pfn > iovad->dma_32bit_pfn) ||
> - (iovad->cached32_node == NULL))
> + if (limit_pfn <= iovad->dma_32bit_pfn)
> + return iovad->cached32_node;
> + else
> + return iovad->cached64_node;
> +}
> +
> +static struct rb_node *
> +__get_cached_rbnode_and_limit(struct iova_domain *iovad,
> + unsigned long *limit_pfn)
> +{
> + struct rb_node *cached_node = __get_cached_rbnode(iovad, *limit_pfn);
> +
> + if (cached_node == NULL) {
> return rb_last(&iovad->rbroot);
> - else {
> - struct rb_node *prev_node = rb_prev(iovad->cached32_node);
> + } else {
> + struct rb_node *prev_node = rb_prev(cached_node);
> struct iova *curr_iova =
> - rb_entry(iovad->cached32_node, struct iova, node);
> + rb_entry(cached_node, struct iova, node);
> *limit_pfn = curr_iova->pfn_lo;
> return prev_node;
> }
> @@ -124,33 +135,50 @@ __get_cached_rbnode(struct iova_domain *iovad, unsigned long *limit_pfn)
>
> static void
> __cached_rbnode_insert_update(struct iova_domain *iovad,
> - unsigned long limit_pfn, struct iova *new)
> + unsigned long limit_pfn, struct rb_node *node)
> {
> - if (limit_pfn != iovad->dma_32bit_pfn)
> - return;
> - iovad->cached32_node = &new->node;
> + if (limit_pfn == iovad->dma_32bit_pfn)
> + iovad->cached32_node = node;
> + else if (limit_pfn > iovad->dma_32bit_pfn)
> + iovad->cached64_node = 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);
> -
> - 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);
> + struct rb_node *cached_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;
> + if (free->pfn_lo <= iovad->dma_32bit_pfn) {
> + if (unlikely(iovad->cached64_node == &free->node))
> + iovad->cached64_node = NULL;
> + cached_node = iovad->cached32_node;
> + if (!cached_node)
> + return;
> + cached_iova = rb_entry(cached_node, struct iova, node);
> + if (free->pfn_lo >= cached_iova->pfn_lo) {
> + struct rb_node *next_node = rb_next(&free->node);
> +
> + if (next_node &&
> + rb_entry(next_node, struct iova, node)->pfn_lo <=
> + iovad->dma_32bit_pfn)
> + iovad->cached32_node = next_node;
> + else
> + iovad->cached32_node = NULL;
> + }
> + } else {
> + cached_node = iovad->cached64_node;
> + if (!cached_node)
> + return;
> + cached_iova = container_of(cached_node, struct iova, node);
> + if (free->pfn_lo >= cached_iova->pfn_lo) {
> + struct rb_node *next_node = rb_next(&free->node);
> +
> + if (next_node)
> + iovad->cached64_node = next_node;
> + else
> + iovad->cached64_node = NULL;
> + }
> }
> }
>
> @@ -204,7 +232,7 @@ 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);
> + curr = __get_cached_rbnode_and_limit(iovad, &limit_pfn);
> prev = curr;
> while (curr) {
> struct iova *curr_iova = rb_entry(curr, struct iova, node);
> @@ -238,7 +266,7 @@ 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, saved_pfn, &new->node);
>
> spin_unlock_irqrestore(&iovad->iova_rbtree_lock, flags);
>
> diff --git a/include/linux/iova.h b/include/linux/iova.h
> index d179b9b..ea89695 100644
> --- a/include/linux/iova.h
> +++ b/include/linux/iova.h
> @@ -71,6 +71,7 @@ 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 *cached64_node; /* Save last alloced node */
> unsigned long granule; /* pfn granularity for this domain */
> unsigned long start_pfn; /* Lower limit for this domain */
> unsigned long dma_32bit_pfn;
> --
> 2.1.2

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