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From: Michael Forney <mforney@mforney.org>
Date: Fri, 4 Feb 2022 18:04:09 -0800
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X-Bullshit: leveraged virtualized SQL over AJAX markup enhancement 
Subject: [9front] qemu clock/timer issue
Reply-To: 9front@9front.org
Precedence: bulk

I was recently running 9front in a VM on linux (qemu, with
-enable-kvm), and noticed several weird timing/clock issues. The date
command gives wildly varying results +- 1 minute:

cpu% date
Fri Feb  4 17:39:23 PST 2022
cpu% date
Fri Feb  4 17:39:12 PST 2022
cpu% date
Fri Feb  4 17:40:19 PST 2022
cpu% date
Fri Feb  4 17:39:18 PST 2022

`sleep 1` exits pretty much instantly, stats moves through the entire
width in a second or two, and clicking in scrollbars starts repeating
immediately.

I notice the following messages in my dmesg:
kvm: vcpu 3: requested 38141 ns lapic timer period limited to 200000 ns
kvm: vcpu 1: requested 9449 ns lapic timer period limited to 200000 ns
kvm: vcpu 2: requested 51204 ns lapic timer period limited to 200000 ns
kvm: vcpu 0: requested 74421 ns lapic timer period limited to 200000 ns

I don't remember this problem last time I ran 9front in qemu (around a
year ago), so I looked through commit history and found one commit
that seemed like it might be related:
http://git.9front.org/plan9front/plan9front/a05bab362f66ddd6fa65f2e7cda9eaaa0217ec08/commit.html

To check, I tried setting *nohpet=1 in my plan9.ini, which *seems* to
have solved the problem, though I still see those same messages in
dmesg on the linux host (but now the requested lapic timer period is
always around 100000 ns or greater).

Anyone know what's going on here?