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SubjectRe: [PATCH] iommu/iova: Improve alloc_iova performance
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I see now that this is redundant with Robin's patch series "Optimise
64-bit IOVA allocations".  I tested those patches on our platform and
find that they solve the performance problem we were having. So, I'd
like to withdraw this patch.

On 9/27/2017 10:10 AM, Joerg Roedel wrote:
> 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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