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

From: Robin Murphy
Date: Wed Jul 19 2017 - 06:23:24 EST


On 19/07/17 09:37, Ard Biesheuvel wrote:
> On 18 July 2017 at 17:57, Robin Murphy <robin.murphy@xxxxxxx> 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@xxxxxxxxxxxxxxxxxxxxxxxxxx/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@xxxxxxxxxx>

Thanks!

Robin.