linux-kernel - Re: [PATCH v2 0/4] Optimise 64-bit IOVA allocations

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Date:   Wed, 26 Jul 2017 13:08:07 +0200
From:   Joerg Roedel <joro@...tes.org>
To:     Robin Murphy <robin.murphy@....com>
Cc:     iommu@...ts.linux-foundation.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        dwmw2@...radead.org, thunder.leizhen@...wei.com,
        lorenzo.pieralisi@....com, ard.biesheuvel@...aro.org,
        Jonathan.Cameron@...wei.com, nwatters@...eaurora.org,
        ray.jui@...adcom.com
Subject: Re: [PATCH v2 0/4] Optimise 64-bit IOVA allocations

Hi Robin.

On Fri, Jul 21, 2017 at 12:41:57PM +0100, Robin Murphy wrote:
> Hi all,
> 
> In the wake of the ARM SMMU optimisation efforts, it seems that certain
> workloads (e.g. storage I/O with large scatterlists) probably remain quite
> heavily influenced by IOVA allocation performance. Separately, Ard also
> reported massive performance drops for a graphical desktop on AMD Seattle
> when enabling SMMUs via IORT, which we traced to dma_32bit_pfn in the DMA
> ops domain getting initialised differently for ACPI vs. DT, and exposing
> the overhead of the rbtree slow path. Whilst we could go around trying to
> close up all the little gaps that lead to hitting the slowest case, it
> seems a much better idea to simply make said slowest case a lot less slow.

Do you have some numbers here? How big was the impact before these
patches and how is it with the patches?


	Joerg