On 19/07/17 09:37, Ard Biesheuvel wrote:

On 18 July 2017 at 17:57, Robin Murphy [off-list ref] wrote:

quoted

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 at 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 <redacted>

Thanks!

Robin.