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    SubjectRe: [RFC] Make need_resched() return true when rcu_urgent_qs requested
    On Mon, Jul 09, 2018 at 11:56:41AM +0100, David Woodhouse wrote:

    > > 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.

    Argh I never found that, because obfuscation:

    ruqp = per_cpu_ptr(&rcu_dynticks.rcu_urgent_qs, rdp->cpu);
    ...
    smp_store_release(ruqp, true);

    I, using git grep "rcu_urgent_qs.*true" only found
    rcu_request_urgent_qs_task() and sync_sched_exp_handler().

    But how come KVM even triggers that case; rcu_implicit_dynticks_qs() is
    for NOHZ and offline CPUs.


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