rcu: Force nohz_full tick on upon irq enter instead of exit (b200a048) · Commits · 戴 / test

There is interrupt-exit code that forces on the tick for nohz_full CPUs failing to respond to the current grace period in a timely fashion. However, this code must compare ->dynticks_nmi_nesting to the value 2 in the interrupt-exit fastpath. This commit therefore moves this code to the interrupt-entry fastpath, where a lighter-weight comparison to zero may be used. Reported-by:

Joel Fernandes <joel@joelfernandes.org> [ paulmck: Apply Joel Fernandes TICK_DEP_MASK_RCU->TICK_DEP_BIT_RCU fix. ] Signed-off-by:

Paul E. McKenney <paulmck@kernel.org>

kernel/rcu/tree.c

+5 −6

Original line number	Diff line number	Diff line
		@@ -651,12 +651,6 @@ static __always_inline void rcu_nmi_exit_common(bool irq)
		*/
		if (rdp->dynticks_nmi_nesting != 1) {
		trace_rcu_dyntick(TPS("--="), rdp->dynticks_nmi_nesting, rdp->dynticks_nmi_nesting - 2, rdp->dynticks);
		if (tick_nohz_full_cpu(rdp->cpu) &&
		rdp->dynticks_nmi_nesting == 2 &&
		rdp->rcu_urgent_qs && !rdp->rcu_forced_tick) {
		rdp->rcu_forced_tick = true;
		tick_dep_set_cpu(rdp->cpu, TICK_DEP_MASK_RCU);
		}
		WRITE_ONCE(rdp->dynticks_nmi_nesting, /* No store tearing. */
		rdp->dynticks_nmi_nesting - 2);
		return;
		@@ -831,6 +825,11 @@ static __always_inline void rcu_nmi_enter_common(bool irq)
		rcu_cleanup_after_idle();

		incby = 1;
		} else if (tick_nohz_full_cpu(rdp->cpu) &&
		rdp->dynticks_nmi_nesting == DYNTICK_IRQ_NONIDLE &&
		rdp->rcu_urgent_qs && !rdp->rcu_forced_tick) {
		rdp->rcu_forced_tick = true;
		tick_dep_set_cpu(rdp->cpu, TICK_DEP_BIT_RCU);
		}
		trace_rcu_dyntick(incby == 1 ? TPS("Endirq") : TPS("++="),
		rdp->dynticks_nmi_nesting,

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