On Tue, Aug 05, 2025 at 10:40:30AM +0200, Gabriele Monaco wrote:

Hello Nam,

I just built and booted up the monitor in a VM (virtme-ng), the
configuration has preemptirq tracepoints and all monitors so far (as we
have seen earlier, it doesn't build if rtapp monitors are not there
because of the circular dependency in the tracepoints).

All I did was to enable the monitor and printk reactor, but I get a
whole lot of errors (as in, I need to quit the VM for it to stop):

[ 1537.699834] rv: rts: 7: violation detected
[ 1537.699930] rv: rts: 3: violation detected
[ 1537.701827] rv: rts: 6: violation detected
[ 1537.704894] rv: rts: 0: violation detected
[ 1537.704925] rv: rts: 0: violation detected
[ 1537.704988] rv: rts: 3: violation detected
[ 1537.705019] rv: rts: 3: violation detected
[ 1537.705998] rv: rts: 0: violation detected
[ 1537.706024] rv: rts: 0: violation detected
[ 1537.709875] rv: rts: 6: violation detected
[ 1537.709921] rv: rts: 6: violation detected
[ 1537.711241] rv: rts: 6: violation detected

Curiously enough, I only see those CPUs (0, 3, 6 and 7).
Other runs have different CPUs but always a small subset (e.g. 10-15,
6-7 only 2).
It doesn't always occur but enabling/disabling the monitor might help
triggering it.

Any idea what is happening?

Thanks for the report. I can reproduce the issue.

Looking at the tracepoints, it makes sense why the monitor complains, some
RT tasks are enqueued but are not dequeued. Then a sched_switch happens
which switches to a non-RT task.

Most likely the dequeue tracepoint misses some cases, let me investigate..

Nam