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Date:   Tue, 12 Jan 2021 16:33:07 +0000
From:   Christoph Hellwig <hch@...radead.org>
To:     Robin Murphy <robin.murphy@....com>
Cc:     "Isaac J. Manjarres" <isaacm@...eaurora.org>, will@...nel.org,
        joro@...tes.org, pdaly@...eaurora.org, pratikp@...eaurora.org,
        linux-arm-kernel@...ts.infradead.org,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 0/5] Optimize iommu_map_sg() performance

On Tue, Jan 12, 2021 at 04:00:59PM +0000, Robin Murphy wrote:
> Out of curiosity, how much of the difference is attributable to actual
> indirect call overhead vs. the additional massive reduction in visits to
> arm_smmu_rpm_{get,put} that you fail to mention? There are ways to optimise
> indirect calling that would benefit *all* cases, rather than just one
> operation for one particular driver.

Do we have systems that use different iommu_ops at the same time?
If not this would be a prime candidate for static call optimizations.

Also I've been pondering adding direct calls to the iommu dma ops like
we do for DMA direct.  This would allow to stop using dma_ops entirely
for arm64.

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