Hi,

On Tue, Jul 13, 2021 at 11:07 AM Robin Murphy [off-list ref] wrote:

On 2021-07-08 15:36, Doug Anderson wrote:
[...]

quoted

quoted

Or document for the users that want performance how to
change the setting, so that they can decide.

Pushing this to the users can make sense for a Linux distribution but
probably less sense for an embedded platform. So I'm happy to make
some way for a user to override this (like via kernel command line),
but I also strongly believe there should be a default that users don't
have to futz with that we think is correct.

FYI I did make progress on the "punt it to userspace" approach. I'm not
posting it even as an RFC yet because I still need to set up a machine
to try actually testing any of it (it's almost certainly broken
somewhere), but in the end it comes out looking surprisingly not too bad
overall. If you're curious to take a look in the meantime I put it here:

https://gitlab.arm.com/linux-arm/linux-rm/-/commits/iommu/fq

Being able to change this at runtime through sysfs sounds great and it
fills all the needs I'm aware of, thanks! In Chrome OS we can just use
this with some udev rules and get everything we need. I'm happy to
give this a spin when you're ready for extra testing.

-Doug