On Mon, Oct 07, 2019 at 08:33:53PM -0700, Paul E. McKenney wrote:
[...]
> > ---
> > kernel/rcu/tree_exp.h | 17 +++++++----------
> > 1 file changed, 7 insertions(+), 10 deletions(-)
> >
> > diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h
> > index af7e7b9c86af..fb51752ac9a6 100644
> > --- a/kernel/rcu/tree_exp.h
> > +++ b/kernel/rcu/tree_exp.h
> > @@ -372,12 +372,10 @@ static void sync_rcu_exp_select_node_cpus(struct
> > work_struct *wp)
> > raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
> >
> > /* IPI the remaining CPUs for expedited quiescent state. */
> > - for_each_leaf_node_cpu_mask(rnp, cpu, rnp->expmask) {
> > + for_each_leaf_node_cpu_mask(rnp, cpu, mask_ofl_ipi) {
> > unsigned long mask = leaf_node_cpu_bit(rnp, cpu);
> > struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
> >
> > - if (!(mask_ofl_ipi & mask))
> > - continue;
> > retry_ipi:
> > if (rcu_dynticks_in_eqs_since(rdp, rdp->exp_dynticks_snap)) {
> > mask_ofl_test |= mask;
>
> This part I have already on -rcu branch "dev".
>
> > @@ -389,10 +387,10 @@ static void sync_rcu_exp_select_node_cpus(struct
> > work_struct *wp)
> > }
> > ret = smp_call_function_single(cpu, rcu_exp_handler, NULL, 0);
> > put_cpu();
> > - if (!ret) {
> > - mask_ofl_ipi &= ~mask;
> > + /* the CPU responses the IPI, and it will report QS itself */
> > + if (!ret)
> > continue;
> > - }
> > +
> > /* Failed, raced with CPU hotplug operation. */
> > raw_spin_lock_irqsave_rcu_node(rnp, flags);
> > if ((rnp->qsmaskinitnext & mask) &&
> > @@ -403,13 +401,12 @@ static void sync_rcu_exp_select_node_cpus(struct
> > work_struct *wp)
> > schedule_timeout_uninterruptible(1);
> > goto retry_ipi;
> > }
> > - /* CPU really is offline, so we can ignore it. */
> > - if (!(rnp->expmask & mask))
> > - mask_ofl_ipi &= ~mask;
> > + /* CPU really is offline, and we need its QS. */
> > + if (rnp->expmask & mask)
> > + mask_ofl_test |= mask;
> > raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
> > }
> > /* Report quiescent states for those that went offline. */
> > - mask_ofl_test |= mask_ofl_ipi;
> > if (mask_ofl_test)
> > rcu_report_exp_cpu_mult(rnp, mask_ofl_test, false);
> > }
>
> Would you be willing to port this optimization on top of current -rcu
> branch "dev" with an suitably modified commit message?
> Sure, will do ;-) Regards, Boqun > Thanx, Paul
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