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rcu: Force nohz_full tick on upon irq enter instead of exit

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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>
This commit is contained in:
Paul E. McKenney 2019-08-15 13:24:49 -07:00
parent 66e4c33b51
commit b200a04895
1 changed files with 5 additions and 6 deletions
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11
kernel/rcu/tree.c
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@ -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,