linux-kernel - [PATCH] drivers/cpuidle: Fix guest_halt_poll

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Date: Fri, 28 Jun 2024 16:49:02 +0800
From: ysay <570260087@...com>
To: rafael@...nel.org
Cc: daniel.lezcano@...aro.org,
	linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	ysay <ysaydong@...il.com>
Subject: [PATCH] drivers/cpuidle: Fix guest_halt_poll_ns failed to take effect

From: ysay <ysaydong@...il.com>

When guest_halt_poll_allow_shrink=N,setting guest_halt_poll_ns
from a large value to 0 does not reset the CPU polling time,
despite guest_halt_poll_ns being intended as a mandatory maximum
time limit.

The problem was situated in the adjust_poll_limit() within
drivers/cpuidle/governors/haltpoll.c:79.

Specifically, when guest_halt_poll_allow_shrink was set to N,
resetting guest_halt_poll_ns to zero did not lead to executing any
section of code that adjusts dev->poll_limit_ns.

The issue has been resolved by relocating the check and assignment for
dev->poll_limit_ns outside of the conditional block.
This ensures that every modification to guest_halt_poll_ns
properly influences the CPU polling time.

Signed-off-by: ysay <ysaydong@...il.com>
---
 drivers/cpuidle/governors/haltpoll.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/drivers/cpuidle/governors/haltpoll.c b/drivers/cpuidle/governors/haltpoll.c
index 663b7f164..99c6260d7 100644
--- a/drivers/cpuidle/governors/haltpoll.c
+++ b/drivers/cpuidle/governors/haltpoll.c
@@ -78,26 +78,22 @@ static int haltpoll_select(struct cpuidle_driver *drv,
 
 static void adjust_poll_limit(struct cpuidle_device *dev, u64 block_ns)
 {
-	unsigned int val;
+	unsigned int val = dev->poll_limit_ns;
 
 	/* Grow cpu_halt_poll_us if
 	 * cpu_halt_poll_us < block_ns < guest_halt_poll_us
 	 */
 	if (block_ns > dev->poll_limit_ns && block_ns <= guest_halt_poll_ns) {
-		val = dev->poll_limit_ns * guest_halt_poll_grow;
+		val *= guest_halt_poll_grow;
 
 		if (val < guest_halt_poll_grow_start)
 			val = guest_halt_poll_grow_start;
-		if (val > guest_halt_poll_ns)
-			val = guest_halt_poll_ns;
 
 		trace_guest_halt_poll_ns_grow(val, dev->poll_limit_ns);
-		dev->poll_limit_ns = val;
 	} else if (block_ns > guest_halt_poll_ns &&
 		   guest_halt_poll_allow_shrink) {
 		unsigned int shrink = guest_halt_poll_shrink;
 
-		val = dev->poll_limit_ns;
 		if (shrink == 0) {
 			val = 0;
 		} else {
@@ -108,8 +104,12 @@ static void adjust_poll_limit(struct cpuidle_device *dev, u64 block_ns)
 		}
 
 		trace_guest_halt_poll_ns_shrink(val, dev->poll_limit_ns);
-		dev->poll_limit_ns = val;
 	}
+
+	if (val > guest_halt_poll_ns)
+		val = guest_halt_poll_ns;
+
+	dev->poll_limit_ns = val;
 }
 
 /**
-- 
2.43.5