linux-kernel - [PATCH] intel_idle: replace conditionals with static_cpu_has(X86_FEATURE

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Date:   Fri,  6 Oct 2017 13:19:45 -0400
From:   Jason Baron <jbaron@...mai.com>
To:     linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        Len Brown <lenb@...nel.org>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>
Subject: [PATCH] intel_idle: replace conditionals with static_cpu_has(X86_FEATURE_ARAT)

If the 'arat' cpu flag is set, then the conditionals in intel_idle() that
guard calling tick_broadcast_enter()/exit() will never be true. Use
static_cpu_has(X86_FEATURE_ARAT) to create a fast path to replace
the conditional.

Signed-off-by: Jason Baron <jbaron@...mai.com>
Cc: Jacob Pan <jacob.jun.pan@...ux.intel.com>
Cc: Len Brown <lenb@...nel.org>
Cc: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
---
 drivers/idle/intel_idle.c | 16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

diff --git a/drivers/idle/intel_idle.c b/drivers/idle/intel_idle.c
index 5dc7ea4..5db5e31 100644
--- a/drivers/idle/intel_idle.c
+++ b/drivers/idle/intel_idle.c
@@ -913,8 +913,7 @@ static __cpuidle int intel_idle(struct cpuidle_device *dev,
 	struct cpuidle_state *state = &drv->states[index];
 	unsigned long eax = flg2MWAIT(state->flags);
 	unsigned int cstate;
-
-	cstate = (((eax) >> MWAIT_SUBSTATE_SIZE) & MWAIT_CSTATE_MASK) + 1;
+	bool uninitialized_var(tick);
 
 	/*
 	 * NB: if CPUIDLE_FLAG_TLB_FLUSHED is set, this idle transition
@@ -923,12 +922,19 @@ static __cpuidle int intel_idle(struct cpuidle_device *dev,
 	 * useful with this knowledge.
 	 */
 
-	if (!(lapic_timer_reliable_states & (1 << (cstate))))
-		tick_broadcast_enter();
+	if (!static_cpu_has(X86_FEATURE_ARAT)) {
+		cstate = (((eax) >> MWAIT_SUBSTATE_SIZE) &
+				MWAIT_CSTATE_MASK) + 1;
+		tick = false;
+		if (!(lapic_timer_reliable_states & (1 << (cstate)))) {
+			tick = true;
+			tick_broadcast_enter();
+		}
+	}
 
 	mwait_idle_with_hints(eax, ecx);
 
-	if (!(lapic_timer_reliable_states & (1 << (cstate))))
+	if (!static_cpu_has(X86_FEATURE_ARAT) && tick)
 		tick_broadcast_exit();
 
 	return index;
-- 
2.6.1