Re: KVM on POWER8 host lock up since 10d91611f426 ("powerpc/64s: Reimplement book3s idle code in C")

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:

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Excerpts from Michal Suchánek's message of October 17, 2020 6:14 am:

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On Mon, Sep 07, 2020 at 11:13:47PM +1000, Nicholas Piggin wrote:

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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