On Mon, Sep 07, 2020 at 11:13:47PM +1000, Nicholas Piggin wrote: > Excerpts from Michael Ellerman's message of August 31, 2020 8:50 pm: > > 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 :/ > > I haven't had any luck yet reproducing this still. Testing with sub > cores of various different combinations, etc. I'll keep trying though. > > I don't know if there's much we can add to debug it. Can we run pdbg > on the BMCs on these things?
I suppose it depends on the machine type? Thanks Michal