On Mon, Aug 31, 2020 at 11:14:18AM +1000, Nicholas Piggin wrote: > 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. It may be possible to set up fadump with a later kernel version that supports it on powernv and dump the whole kernel.
Thanks Michal