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Date:   Fri, 26 Aug 2022 18:28:39 +0800
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Subject: Re: [PATCH v2] iommu/iova: Optimize alloc_iova with rbtree_augmented
To:     Ethan Zhao <haifeng.zhao@linux.intel.com>, joro@8bytes.org,
        will@kernel.org
Cc:     iommu@lists.linux.dev, linux-kernel@vger.kernel.org,
        robin.murphy@arm.com
References: <20220824095139.66477-1-zhangpeng.00@bytedance.com>
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From:   Peng Zhang <zhangpeng.00@bytedance.com>
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> 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.

Thanks,

Peng