Re: What to do about "WARNING: negative runtime; monotonic clock has gone backwards"

[Taylor R Campbell <riastradh%NetBSD.org@localhost>]

> Date: Wed, 04 Jan 2023 14:43:25 -0500
> From: Brad Spencer <brad%anduin.eldar.org@localhost>
> 
> So...  I have a PV+PVSHIM DOMU running a pretty recent 9.x on a DOM0
> running a 9.99.xx kernel.  The DOM0 is not large, a 4 processor E-2224
> with 32GB of memory.  The DOMU has 2 VCPUs and 8GB of memory.  About
> every day a very particular DOMU tosses the:
> 
> WARNING: negative runtime; monotonic clock has gone backwards

Does this still happen?

Can you either:

1. share the output of `vmstat -e | grep -e tsc -e systime -e
   hardclock' after you get the console warning;

2. run

   dtrace -n 'sdt:xen:clock: { printf("%d %d %d %d %d %d %d",
   arg0, arg1, arg2, arg3, arg4, arg5, arg6, arg7) }'

   on the system, and leave it running with output directed to a file,
   and share the output when you see the console warning; or

3. put `#define XEN_CLOCK_DEBUG 1' in sys/arch/xen/xen/xen_clock.c and
   build a new kernel, and share the dmesg output when you get the
   console warning?

This should tell us whether it's the Xen host's fault or something
wrong in NetBSD.