On Thu, 2018-07-19 at 08:45 +0200, Christian Borntraeger wrote: > > > My thought would be something like this: > > > > if (context_tracking_cpu_is_enabled()) > > rcu_kvm_enter(); > > else > > rcu_virt_note_context_switch(smp_processor_id()); > > In the past we needed that (when we introduced that). At least with every > host interrupt we called this making an rcu event at least every HZ. > Will the changes in need_resched make this part unnecessary? Yes, the change in need_resched() should make this part unnecessary. Unless your architecture's version of the vcpu_run() loop just loops forever even when TIF_NEED_RESCHED is set? :) I'm not sure about the context tracking condition in the code snippet cited above, though. I think that's what caused my problem in the first place — I have CONTEXT_TRACKING_FORCE && !NO_HZ_FULL. So in 4.15, that means rcu_user_enter() did nothing and rcu_virt_note_context_switch() wasn't called. Hence the observed stalls. Should rcu_user_enter() itself be conditional on CONTEXT_TRACKING not NO_HZ_FULL?
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