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[3/3] cpuidle: powerpc: no memory barrier after break from idle

Message ID 20170614130241.19865-4-npiggin@gmail.com (mailing list archive)
State Not Applicable, archived
Delegated to: Rafael Wysocki
Headers show

Commit Message

Nicholas Piggin June 14, 2017, 1:02 p.m. UTC 
A memory barrier is not required after the task wakes up,
only if we clear the polling flag before waking. The case
where we have work to do is the important one, so optimise
for it.

Reviewed-by: Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
---
 drivers/cpuidle/cpuidle-powernv.c | 11 +++++++++--
 drivers/cpuidle/cpuidle-pseries.c | 11 +++++++++--
 2 files changed, 18 insertions(+), 4 deletions(-)
diff mbox

Patch

diff --git a/drivers/cpuidle/cpuidle-powernv.c b/drivers/cpuidle/cpuidle-powernv.c
index abf2ffcd4a0a..722b81b03593 100644
--- a/drivers/cpuidle/cpuidle-powernv.c
+++ b/drivers/cpuidle/cpuidle-powernv.c
@@ -59,14 +59,21 @@  static int snooze_loop(struct cpuidle_device *dev,
 	ppc64_runlatch_off();
 	HMT_very_low();
 	while (!need_resched()) {
-		if (likely(snooze_timeout_en) && get_tb() > snooze_exit_time)
+		if (likely(snooze_timeout_en) && get_tb() > snooze_exit_time) {
+			/*
+			 * Task has not woken up but we are exiting the polling
+			 * loop anyway. Require a barrier after polling is
+			 * cleared to order subsequent test of need_resched().
+			 */
+			clear_thread_flag(TIF_POLLING_NRFLAG);
+			smp_mb();
 			break;
+		}
 	}
 
 	HMT_medium();
 	ppc64_runlatch_on();
 	clear_thread_flag(TIF_POLLING_NRFLAG);
-	smp_mb();
 
 	return index;
 }
diff --git a/drivers/cpuidle/cpuidle-pseries.c b/drivers/cpuidle/cpuidle-pseries.c
index a404f352d284..e9b3853d93ea 100644
--- a/drivers/cpuidle/cpuidle-pseries.c
+++ b/drivers/cpuidle/cpuidle-pseries.c
@@ -71,13 +71,20 @@  static int snooze_loop(struct cpuidle_device *dev,
 	while (!need_resched()) {
 		HMT_low();
 		HMT_very_low();
-		if (snooze_timeout_en && get_tb() > snooze_exit_time)
+		if (likely(snooze_timeout_en) && get_tb() > snooze_exit_time) {
+			/*
+			 * Task has not woken up but we are exiting the polling
+			 * loop anyway. Require a barrier after polling is
+			 * cleared to order subsequent test of need_resched().
+			 */
+			clear_thread_flag(TIF_POLLING_NRFLAG);
+			smp_mb();
 			break;
+		}
 	}
 
 	HMT_medium();
 	clear_thread_flag(TIF_POLLING_NRFLAG);
-	smp_mb();
 
 	idle_loop_epilog(in_purr);