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From: Mihai Carabas <mihai.carabas@oracle.com>
To: linux-arm-kernel@lists.infradead.org
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Subject: [PATCH v4 7/8] cpuidle/poll_state: replace cpu_relax with smp_cond_load_relaxed
Date: Thu, 15 Feb 2024 09:41:49 +0200
Message-Id: <1707982910-27680-8-git-send-email-mihai.carabas@oracle.com>
In-Reply-To: <1707982910-27680-1-git-send-email-mihai.carabas@oracle.com>
References: <1707982910-27680-1-git-send-email-mihai.carabas@oracle.com>
Precedence: bulk

cpu_relax on ARM64 does a simple "yield". Thus we replace it with
smp_cond_load_relaxed which basically does a "wfe".

Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Mihai Carabas <mihai.carabas@oracle.com>
---
 drivers/cpuidle/poll_state.c | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/drivers/cpuidle/poll_state.c b/drivers/cpuidle/poll_state.c
index 9b6d90a72601..1e45be906e72 100644
--- a/drivers/cpuidle/poll_state.c
+++ b/drivers/cpuidle/poll_state.c
@@ -13,6 +13,7 @@
 static int __cpuidle poll_idle(struct cpuidle_device *dev,
 			       struct cpuidle_driver *drv, int index)
 {
+	unsigned long ret;
 	u64 time_start;
 
 	time_start = local_clock_noinstr();
@@ -26,12 +27,16 @@ static int __cpuidle poll_idle(struct cpuidle_device *dev,
 
 		limit = cpuidle_poll_time(drv, dev);
 
-		while (!need_resched()) {
-			cpu_relax();
-			if (loop_count++ < POLL_IDLE_RELAX_COUNT)
-				continue;
-
+		for (;;) {
 			loop_count = 0;
+
+			ret = smp_cond_load_relaxed(&current_thread_info()->flags,
+						    VAL & _TIF_NEED_RESCHED ||
+						    loop_count++ >= POLL_IDLE_RELAX_COUNT);
+
+			if (!(ret & _TIF_NEED_RESCHED))
+				break;
+
 			if (local_clock_noinstr() - time_start > limit) {
 				dev->poll_time_limit = true;
 				break;
-- 
1.8.3.1