On Mon, Oct 19, 2020 at 02:50:51PM +1000, Nicholas Piggin wrote:
> Excerpts from Nicholas Piggin's message of October 19, 2020 11:00 am:
> > Excerpts from Michal Suchánek's message of October 17, 2020 6:14 am:
> >> On Mon, Sep 07, 2020 at 11:13:47PM +1000, Nicholas Piggin wrote:

> >>> 
> >>> I haven't had any luck yet reproducing this still. Testing with sub 
> >>> cores of various different combinations, etc. I'll keep trying though.
> >> 
> >> Hello,
> >> 
> >> I tried running some KVM guests to simulate the workload and what I get
> >> is guests failing to start with a rcu stall. Tried both 5.3 and 5.9
> >> kernel and qemu 4.2.1 and 5.1.0
> >> 
> >> To start some guests I run
> >> 
> >> for i in $(seq 0 9) ; do /opt/qemu/bin/qemu-system-ppc64 -m 2048 -accel kvm -smp 8 -kernel /boot/vmlinux -initrd /boot/initrd -nodefaults -nographic -serial mon:telnet::444$i,server,wait & done
> >> 
> >> To simulate some workload I run
> >> 
> >> xz -zc9T0 < /dev/zero > /dev/null &
> >> while true; do
> >>     killall -STOP xz; sleep 1; killall -CONT xz; sleep 1;
> >> done &
> >> 
> >> on the host and add a job that executes this to the ramdisk. However, most
> >> guests never get to the point where the job is executed.
> >> 
> >> Any idea what might be the problem?
> > 
> > I would say try without pv queued spin locks (but if the same thing is 
> > happening with 5.3 then it must be something else I guess). 
> > 
> > I'll try to test a similar setup on a POWER8 here.
> 
> Couldn't reproduce the guest hang, they seem to run fine even with 
> queued spinlocks. Might have a different .config.
> 
> I might have got a lockup in the host (although different symptoms than 
> the original report). I'll look into that a bit further.

Hello,

attaching the config for reference.

I am running with --smt=off because KVM refuses to start VMs otherwise.

Thanks

Michal