Hi all,

Waiting for the command queue to drain for CMD_SYNC completion is likely
a contention hotspot on high-core-count systems. If the SMMU is coherent
and supports MSIs, though, we can use this cool feature (as suggested by
the architecture, no less) to make syncs effectively non-blocking for
anyone other than the caller.

I don't have any hardware that supports MSIs, but this has at least
passed muster on the Fast Model with cache modelling enabled - I'm hoping
the Qualcomm machines have the appropriate configuration to actually test
how well it works in reality. If it is worthwhile, I do have most of a
plan for how we can do something similar in the non-MSI polling case (it's
mostly a problem of handling the queue-wrapping edge cases correctly).

Robin.


Robin Murphy (3):
  iommu/arm-smmu-v3: Specialise CMD_SYNC handling
  iommu/arm-smmu-v3: Forget about cmdq-sync interrupt
  iommu/arm-smmu-v3: Utilise CMD_SYNC MSI feature

 drivers/iommu/arm-smmu-v3.c | 117 +++++++++++++++++++++++++++++---------------
 1 file changed, 77 insertions(+), 40 deletions(-)

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2.13.4.dirty