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SubjectRe: [PATCH v2] iommu/iova: Optimize alloc_iova with rbtree_augmented
On 26/08/2022 11:28, Peng Zhang wrote:
>
>> Though only 3-4 drivers use alloc_iova() directly, in my understanding
>>
>> your test has simulated the worst case, rcache doesn't work at all,
>>
>> "alloc_iova" +“remove_iova” number looks great for worst case.
>
> There is another case, when the size to allocate greater to 2^5, even if
> alloc_iova_fast() is used, alloc_iova() will always be called because
> the maximum iova size that rcache supports to allocate is 32.
> IOVA_RANGE_CACHE_MAX_SIZE specifies the maximum size.
>


If you really have a performance issue with alloc_iova_fast() ->
alloc_iova() then I suggest that you consider trying to use
dma_opt_mapping_size() to teach the DMA engine driver to not create
requests whose overall size exceeds to the rcache limit.

Thanks,
John

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