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

[Michael Ellerman]

Ruediger Oertel <ro at suse.de> writes:
> Am 31.08.20 um 03:14 schrieb Nicholas Piggin:
>> Excerpts from Michal Suchánek's message of August 31, 2020 6:11 am:
>>> Hello,
>>>
>>> on POWER8 KVM hosts lock up since commit 10d91611f426 ("powerpc/64s:
>>> Reimplement book3s idle code in C").
>>>
>>> The symptom is host locking up completely after some hours of KVM
>>> workload with messages like
>>>
>>> 2020-08-30T10:51:31+00:00 obs-power8-01 kernel: KVM: couldn't grab cpu 47
>>> 2020-08-30T10:51:31+00:00 obs-power8-01 kernel: KVM: couldn't grab cpu 71
>>> 2020-08-30T10:51:31+00:00 obs-power8-01 kernel: KVM: couldn't grab cpu 47
>>> 2020-08-30T10:51:31+00:00 obs-power8-01 kernel: KVM: couldn't grab cpu 71
>>> 2020-08-30T10:51:31+00:00 obs-power8-01 kernel: KVM: couldn't grab cpu 47
>>>
>>> printed before the host locks up.
>>>
>>> The machines run sandboxed builds which is a mixed workload resulting in
>>> IO/single core/mutiple core load over time and there are periods of no
>>> activity and no VMS runnig as well. The VMs are shortlived so VM
>>> setup/terdown is somewhat excercised as well.
>>>
>>> POWER9 with the new guest entry fast path does not seem to be affected.
>>>
>>> Reverted the patch and the followup idle fixes on top of 5.2.14 and
>>> re-applied commit a3f3072db6ca ("powerpc/powernv/idle: Restore IAMR
>>> after idle") which gives same idle code as 5.1.16 and the kernel seems
>>> stable.
>>>
>>> Config is attached.
>>>
>>> I cannot easily revert this commit, especially if I want to use the same
>>> kernel on POWER8 and POWER9 - many of the POWER9 fixes are applicable
>>> only to the new idle code.
>>>
>>> Any idea what can be the problem?
>> 
>> So hwthread_state is never getting back to to HWTHREAD_IN_IDLE on
>> those threads. I wonder what they are doing. POWER8 doesn't have a good
>> NMI IPI and I don't know if it supports pdbg dumping registers from the
>> BMC unfortunately. Do the messages always come in pairs of CPUs?
>> 
>> I'm not sure where to start with reproducing, I'll have to try. How many
>> vCPUs in the guests? Do you have several guests running at once?
>
> Hello all,
>
> some details on the setup...
> these machines are buildservice workers, (build.opensuse.org) and all they
> do is spawn new VMs, run a package building job inside (rpmbuild, debbuild,...)
>
> The machines are running in OPAL/PowerNV mode, with "ppc64_cpu --smt=off".
> The number of VMs varies across the machines:
> obs-power8-01: 18 instances, "-smp 16,threads=8"
> obs-power8-02: 20 instances, "-smp 8,threads=8"
> obs-power8-03: 30 instances, "-smp 8,threads=8"
> obs-power8-04: 20 instances, "-smp 8,threads=8"

Can you send us the output of:

# grep . /sys/module/kvm_hv/parameters/*

cheers