Messages in this thread | | | Date | Thu, 1 Sep 2022 11:45:58 +0100 | From | John Garry <> | Subject | Re: [PATCH v2] iommu/iova: Optimize alloc_iova with rbtree_augmented |
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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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