Hi Janne,
On 2020-06-04 12:21, Janne Karhunen wrote:
Hi,
I have an issue on one particular hardware with gicv3 and the old
stable (4.9.22x) kernel where the timer interrupt randomly leaks to
the host after the guest exit and the kvm_arch_timer_handler gets
triggered. The guest does run, but the whine (unexpected interrupt) is
annoying and it seems to be hindering the performance drastically - of
both the host and the guest. This behavior can even lead to the host
watchdog biting as the firing timer prevents the progress, especially
during the very early boot when the guest is doing heavy paging
anyway.
The only system I witnessed this was a Cavium TX1. It seems incredibly
bad at retiring an interrupt that has been masked at the source.
Which hardware is that?
Based on the comment in the latest code the fundamental issue is that
the interrupt controller does not recognize the timer disable fast
enough on guest exit.
Has anyone worked on a proper fix for the issue
for the old stable series? 5+ kernels seem to have quite a drastic
rework on this front. Plain 'isb' did not seem to do the trick after
the timer disable...
ISB really has no bearing on how an interrupt gets retired from the
redistributor. The flow we use on mainline these days makes it less
susceptible to this kind of brokenness, but it is still possible to
hit it.
In general, 4.9 is getting pretty old, and only gets things like
security fixes. Quality of emulation issues are definitely not
getting backported.
Thanks,
M.
--
Jazz is not dead. It just smells funny...
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