[PATCH 0/3] iommu: Avoid DMA ops domain refcount contention

On 14/08/2018 14:04, Robin Murphy wrote:

John raised the issue[1] that we have some unnecessary refcount contention
in the DMA ops path which shows scalability problems now that we have more
real high-performance hardware using iommu-dma. The x86 IOMMU drivers are
sidestepping this by stashing domain references in archdata, but since
that's not very nice for architecture-agnostic code, I think it's time to
look at a generic API-level solution.

These are a couple of quick patches based on the idea I had back when
first implementing this lot, but didn't have any way to justify at the
time. The third patch can be ignored for the sake of API discussion, but
is included for completeness.

Robin.


[1] https://lists.linuxfoundation.org/pipermail/iommu/2018-August/029303.html

Robin Murphy (3):
  iommu: Add fast hook for getting DMA domains
  iommu/dma: Use fast DMA domain lookup
  arm64/dma-mapping: Mildly optimise non-coherent IOMMU ops

 arch/arm64/mm/dma-mapping.c | 10 +++++-----
 drivers/iommu/dma-iommu.c   | 23 ++++++++++++-----------
 drivers/iommu/iommu.c       |  9 +++++++++
 include/linux/iommu.h       |  1 +
 4 files changed, 27 insertions(+), 16 deletions(-)

Thanks Robin. So we'll test this now. I anticipate a decent improvement 
across the board since we are now simply dereferencing the device's 
iommu group directly.

Cheers,
John