From: Marc Zyngier <maz@kernel.org>
To: Janne Karhunen <janne.karhunen@gmail.com>
Cc: kvmarm@lists.cs.columbia.edu
Subject: Re: randomly firing kvm_arch_timer_handler
Date: Thu, 04 Jun 2020 13:37:50 +0100 [thread overview]
Message-ID: <7d05e422cb61296fe372e0de3f1602b2@kernel.org> (raw)
In-Reply-To: <CAE=Ncrb80uS5wtAu6e1Gctnu8tjcBEpWd7zHJv7aHdEkipe2FQ@mail.gmail.com>
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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next prev parent reply other threads:[~2020-06-04 12:37 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-04 11:21 randomly firing kvm_arch_timer_handler Janne Karhunen
2020-06-04 12:37 ` Marc Zyngier [this message]
2020-06-04 13:14 ` Janne Karhunen
2020-06-09 5:49 ` Janne Karhunen
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