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    SubjectRe: [RFC] Make need_resched() return true when rcu_urgent_qs requested
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    On Mon, 2018-07-09 at 12:44 +0200, Peter Zijlstra wrote:
    > On Mon, Jul 09, 2018 at 10:18:55AM +0100, David Woodhouse wrote:
    > >
    > > >
    > > > Which seems like an entirely reasonable amount of time to kick a task.
    > > > Not scheduling for a second is like an eternity.
    > >
    > > If that is our only "fix" for KVM, then wouldn't that mean that things
    > > like expand_fdtable() would be *expected* to take "an eternity" when
    > > another CPU happens to be in the guest? Because vcpu_run() would still
    > > loop until the task gets kicked after a second?
    >
    > But either proposal is exactly the same in this respect. The whole
    > rcu_urgent_qs thing won't be set any earlier either.

    Er.... Marius, our latencies in expand_fdtable() definitely went from
    ~10s to well below one second when we just added the rcu_all_qs() into
    the loop, didn't they? And that does nothing if !rcu_urgent_qs.

    Doesn't rcu_implicit_dynticks_qs() set it after jiffies_till_sched_qs
    (default HZ/10) has expired?
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