Messages in this thread | | | Subject | Re: [PATCH v2] kvm/x86: Inform RCU of quiescent state when entering guest mode | From | David Woodhouse <> | Date | Thu, 12 Jul 2018 09:31:28 +0100 |
| |
On Wed, 2018-07-11 at 16:47 -0700, Paul E. McKenney wrote: > > > > What changed was RCU's reactions to longish grace periods. It used to > > > be very aggressive about forcing the scheduler to do otherwise-unneeded > > > context switches, which became a problem somewhere between v4.9 and v4.15. > > > I therefore reduced the number of such context switches, which in turn > > > caused KVM to tell RCU about quiescent states way too infrequently. > > > > You talk about > > commit bcbfdd01dce5556a952fae84ef16fd0f12525e7b > > rcu: Make non-preemptive schedule be Tasks RCU quiescent state > > > > correct? In fact, then whatever (properly sent) patch comes up should contain > > a fixes tag. > > Not that one, but this one is at least part of the "team": > > 28053bc72c0e5 ("rcu: Add long-term CPU kicking"). I might need to use > "git bisect" to find the most relevant commit... :-/
Whichever commit we blame, I suspect the Fixes: tag wants to go on Paul's earlier 'Make need_resched() respond to urgent RCU-QS needs' patch.
The rcu_kvm_enter() thing we're talking about now is actually addressing a problem which has existed for much longer — that with NO_HZ_FULL, a CPU might end up in guest mode for an indefinite period of time, with RCU waiting for it to return.[unhandled content-type:application/x-pkcs7-signature]
| |