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    SubjectRe: [PATCH v2] kvm/x86: Inform RCU of quiescent state when entering guest mode
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    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]
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