On 27/05/21 12:17, Marc Zyngier wrote:

On Tue, 25 May 2021 18:32:45 +0100,
Valentin Schneider [off-list ref] wrote:

quoted

I've tested this on my Ampere eMAG, which uncovered "fun" interactions with
the MSI domains. Did the same trick as the Juno with the pl011.

pNMIs cause said eMAG to freeze, but that's true even without my patches. I
did try them out under QEMU+KVM and that looked fine, although that means I
only got to test EOImode=0. I'll try to dig into this when I get some more
cycles.

That's interesting/worrying. As far as I remember, this machine uses
GIC500, which is a well known quantity. If pNMIs are causing issues,
that'd probably be a CPU interface problem. Can you elaborate on how
you tried to test that part? Just using the below benchmark?

Not even that, it would hang somewhere at boot. Julien suggested offline
that it might be a problem with the secondaries' PMR initial value, but I
really never got to do dig into it.

quoted

Performance impact
==================

Benchmark
+++++++++

Finding a benchmark that leverages a force-threaded IRQ has proved to be
somewhat of a pain, so I crafted my own. It's a bit daft, but so are most
benchmarks (though this one might win a prize).

I love it (and wrote similar hacks in my time)! :D

Yay!

Can you put that up
somewhere so that I can run the same test on my own zoo and find out
how it fares?

The setup part is really fugly and I was too ashamed of it to link it in
the cover letter; for ACPI I could simply use acpi_register_gsi() since
that uses the right domain by default, but for DT I ended up adding a DT
entry and a match table.

I'll see about unifying this and I'll send it out your way.

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