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

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Date:   Wed, 19 Jul 2017 11:23:12 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc:     Joerg Roedel <joro@...tes.org>, iommu@...ts.linux-foundation.org,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        David Woodhouse <dwmw2@...radead.org>,
        Zhen Lei <thunder.leizhen@...wei.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Jonathan.Cameron@...wei.com, nwatters@...eaurora.org,
        ray.jui@...adcom.com
Subject: Re: [PATCH 0/4] Optimise 64-bit IOVA allocations

On 19/07/17 09:37, Ard Biesheuvel wrote:
> On 18 July 2017 at 17:57, Robin Murphy <robin.murphy@....com> 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.
>>
>> I had a go at rebasing Leizhen's last IOVA series[1], but ended up finding
>> the changes rather too hard to follow, so I've taken the liberty here of
>> picking the whole thing up and reimplementing the main part in a rather
>> less invasive manner.
>>
>> Robin.
>>
>> [1] https://www.mail-archive.com/iommu@lists.linux-foundation.org/msg17753.html
>>
>> Robin Murphy (1):
>>   iommu/iova: Extend rbtree node caching
>>
>> Zhen Lei (3):
>>   iommu/iova: Optimise rbtree searching
>>   iommu/iova: Optimise the padding calculation
>>   iommu/iova: Make dma_32bit_pfn implicit
>>
>>  drivers/gpu/drm/tegra/drm.c      |   3 +-
>>  drivers/gpu/host1x/dev.c         |   3 +-
>>  drivers/iommu/amd_iommu.c        |   7 +--
>>  drivers/iommu/dma-iommu.c        |  18 +------
>>  drivers/iommu/intel-iommu.c      |  11 ++--
>>  drivers/iommu/iova.c             | 112 ++++++++++++++++-----------------------
>>  drivers/misc/mic/scif/scif_rma.c |   3 +-
>>  include/linux/iova.h             |   8 +--
>>  8 files changed, 60 insertions(+), 105 deletions(-)
>>
> 
> These patches look suspiciously like the ones I have been using over
> the past couple of weeks (modulo the tegra and host1x changes) from
> your git tree. They work fine on my AMD Overdrive B1, both in DT and
> in ACPI/IORT modes, although it is difficult to quantify any
> performance deltas on my setup.

Indeed - this is a rebase (to account for those new callers) with a
couple of trivial tweaks to error paths and corner cases that normal
usage shouldn't have been hitting anyway. "No longer unusably awful" is
a good enough performance delta for me :)

> Tested-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>

Thanks!

Robin.