Michal Suchánek <msucha...@suse.de> writes: > 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.
Your firmware won't support it AFAIK. You could try kdump, but if we have CPUs stuck in KVM then there's a good chance it won't work :/ cheers