On Tue, May 10, 2022 at 06:07:00PM +0000, Rik van Riel wrote: > On Tue, 2022-05-10 at 09:52 -0700, Josh Poimboeuf wrote: > > On Tue, May 10, 2022 at 04:07:42PM +0000, Rik van Riel wrote: > > > > > > > Now I wonder if we could just hook up a preempt notifier > > > for kernel live patches. All the distro kernels already > > > need the preempt notifier for KVM, anyway... > > > > > > > I wouldn't be opposed to that, but how does it solve this problem? > > If > > as Peter said cond_resched() can be a NOP, then preemption would have > > to > > be from an interrupt, in which case frame pointers aren't reliable. > > > The systems where we are seeing problems do not, as far > as I know, throw softlockup errors, so the kworker > threads that fail to transition to the new KLP version > are sleeping and getting scheduled out at times. Are they sleeping due to an explicit call to cond_resched()? > A KLP transition preempt notifier would help those > kernel threads transition to the new KLP version at > any time they reschedule. ... unless cond_resched() is a no-op due to CONFIG_PREEMPT? > How much it will help is hard to predict, but I should > be able to get results from a fairly large sample size > of systems within a few weeks :) As Peter said, keep in mind that we will need to fix other cases beyond Facebook, i.e., CONFIG_PREEMPT combined with non-x86 arches which don't have ORC so they can't reliably unwind from an IRQ. -- Josh
