On Sat, Aug 03, 2024 at 11:23:21AM +0200, Claudio Fontana wrote:
> Hello Stefan,
>
> did not know where to report this, but the man page mentions you specifically so here I am.
Hi Claudio,
I wrote the man page for kvm_stat(1) but am not the maintainer of the
tool. I have CCed the KVM mailing list although it's possible that no
one actively maintains the tool :).
>
>
> There seems to be an issue when kvm_stat is run with:
>
> kvm_stat -p xxx -d -t -s yy -c -L FILENAME.csv &
>
> specifically due to the ampersand (&), thus running in the background.
>
>
> It seems that kvm_stat gets the interrupt signal (SIGINT), and does write as a result the output to disk,
> but then instead of terminating, it just hangs there forever.
That is strange. The only signal handler installed by kvm_stat is for
SIGHUP, so Python should perform the default behavior for SIGINT and
terminate. I'm not sure why the process would hang.
>
> So to avoid ending up with a large number of kvm_stat processes lingering on the system,
> we needed to put a random sleep, and then send a SIGTERM to terminate the kvm_stat processes.
>
> Just sending a SIGTERM (without the SIGINT) does terminate the kvm_stat processes, but NO DATA is written to disk (the files show as 0 size).
That makes sense since kvm_stat does not handle SIGTERM. The default
SIGTERM behavior is to terminal and any output in Python's I/O buffers
may not have been written to the file.
Maybe kvm_stat should catch SIGINT and SIGTERM. That would give it a
chance to write out the log before terminating. Do you want to try
implementing that?
>
> This is the workaround script that we currently have:
>
> ----
>
> #! /bin/bash
>
> VM_PIDS=`pgrep qemu-system-`
>
> for VM_PID in ${VM_PIDS} ; do
> # warning: kvm_stat is very fragile, change with care
> kvm_stat -p ${VM_PID} -d -t -s 1 -c -L kvm_stat_${VM_PID}.csv &
> done
>
> if test "x${VM_PID}" != "x" ; then
> echo "launched kvm_stat processes, capturing 10 seconds..."
> sleep 10
> echo "signaling all kvm_stat processes to write to disk..."
> pkill -INT -P $$
> sleep 5
> sync
> echo "signaling all kvm_stat processes to die..."
> pkill -TERM -P $$
> echo "waiting for kvm_stat processes to exit..."
> while pgrep -P $$ > /dev/null; do
> sleep 2
> echo "still waiting for kvm_stat processes to exit..."
> done
> fi
>
> echo "Done."
>
> ----
>
> Feel free to forward to the appropriate mailing list if needed,
>
> thanks!
>
> Claudio
>
> --
> Claudio Fontana
> Engineering Manager Virtualization, SUSE Labs Core
>
> SUSE Software Solutions Italy Srl
>
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