On (03/23/15 09:02), Benjamin Herrenschmidt wrote:

quoted

How does this relate to the ARM implementation? There is currently
an effort going on to make that one shared with ARM64 and possibly
x86. Has anyone looked at both the PowerPC and ARM ways of doing the
allocation to see if we could pick one of the two to work on
all architectures?

What I see in ARM is horribly complex, I can't quite make sense of it
in a couple of minutes of looking at it, and doesn't seem to address the
basic issue we are addressing here which is the splitting of the iommu
table lock.

Amen to that.. I thought it was just me :-)

I plan to go through the code to see if/where the armd iommu code
does its locking and achieves its parallelism, but the mapping
between the sparc/powerpc approach and armd is not immediately obvious
to me.

--Sowmini