linux-kernel - [PATCH 5/5] cpuidle: Handle TIF_NR_POLLING on behalf of software polling idle states

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Message-ID: <20241206130408.18690-6-frederic@kernel.org>
Date: Fri,  6 Dec 2024 14:04:08 +0100
From: Frederic Weisbecker <frederic@...nel.org>
To: LKML <linux-kernel@...r.kernel.org>
Cc: Frederic Weisbecker <frederic@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	"Rafael J . Wysocki" <rafael@...nel.org>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	linux-pm@...r.kernel.org,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>
Subject: [PATCH 5/5] cpuidle: Handle TIF_NR_POLLING on behalf of software polling idle states

Software polling idle states set again TIF_NR_POLLING and clear it upon
exit. This involves error prone duplicated code and wasted cycles
performing atomic operations, sometimes RmW fully ordered.

To avoid this, benefit instead from the same generic TIF_NR_POLLING
handling that is currently in use for hardware monitoring states.

Signed-off-by: Frederic Weisbecker <frederic@...nel.org>
---
 drivers/cpuidle/cpuidle-powernv.c | 10 ----------
 drivers/cpuidle/cpuidle-pseries.c | 11 -----------
 drivers/cpuidle/cpuidle.c         |  2 +-
 drivers/cpuidle/poll_state.c      | 30 ++++++++++++------------------
 4 files changed, 13 insertions(+), 40 deletions(-)

diff --git a/drivers/cpuidle/cpuidle-powernv.c b/drivers/cpuidle/cpuidle-powernv.c
index 9ebedd972df0..1bf0d2234016 100644
--- a/drivers/cpuidle/cpuidle-powernv.c
+++ b/drivers/cpuidle/cpuidle-powernv.c
@@ -71,8 +71,6 @@ static int snooze_loop(struct cpuidle_device *dev,
 {
 	u64 snooze_exit_time;
 
-	set_thread_flag(TIF_POLLING_NRFLAG);
-
 	local_irq_enable();
 
 	snooze_exit_time = get_tb() + get_snooze_timeout(dev, drv, index);
@@ -81,21 +79,13 @@ static int snooze_loop(struct cpuidle_device *dev,
 	HMT_very_low();
 	while (!need_resched()) {
 		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);
 			dev->poll_time_limit = true;
-			smp_mb();
 			break;
 		}
 	}
 
 	HMT_medium();
 	ppc64_runlatch_on();
-	clear_thread_flag(TIF_POLLING_NRFLAG);
 
 	local_irq_disable();
 
diff --git a/drivers/cpuidle/cpuidle-pseries.c b/drivers/cpuidle/cpuidle-pseries.c
index f68c65f1d023..704bb01d9e9e 100644
--- a/drivers/cpuidle/cpuidle-pseries.c
+++ b/drivers/cpuidle/cpuidle-pseries.c
@@ -40,8 +40,6 @@ int snooze_loop(struct cpuidle_device *dev, struct cpuidle_driver *drv,
 {
 	u64 snooze_exit_time;
 
-	set_thread_flag(TIF_POLLING_NRFLAG);
-
 	pseries_idle_prolog();
 	raw_local_irq_enable();
 	snooze_exit_time = get_tb() + snooze_timeout;
@@ -51,21 +49,12 @@ int snooze_loop(struct cpuidle_device *dev, struct cpuidle_driver *drv,
 		HMT_low();
 		HMT_very_low();
 		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().
-			 */
 			dev->poll_time_limit = true;
-			clear_thread_flag(TIF_POLLING_NRFLAG);
-			smp_mb();
 			break;
 		}
 	}
 
 	HMT_medium();
-	clear_thread_flag(TIF_POLLING_NRFLAG);
-
 	raw_local_irq_disable();
 
 	pseries_idle_epilog();
diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c
index 46c0a2726f67..fecc50c2860e 100644
--- a/drivers/cpuidle/cpuidle.c
+++ b/drivers/cpuidle/cpuidle.c
@@ -237,7 +237,7 @@ noinstr int cpuidle_enter_state(struct cpuidle_device *dev,
 		broadcast = false;
 	}
 
-	polling = target_state->flags & CPUIDLE_FLAG_MWAIT;
+	polling = target_state->flags & (CPUIDLE_FLAG_MWAIT | CPUIDLE_FLAG_POLLING);
 
 	/*
 	 * If the target state doesn't poll on need_resched(), this is
diff --git a/drivers/cpuidle/poll_state.c b/drivers/cpuidle/poll_state.c
index 9b6d90a72601..d69936e2517e 100644
--- a/drivers/cpuidle/poll_state.c
+++ b/drivers/cpuidle/poll_state.c
@@ -13,35 +13,29 @@
 static int __cpuidle poll_idle(struct cpuidle_device *dev,
 			       struct cpuidle_driver *drv, int index)
 {
-	u64 time_start;
-
-	time_start = local_clock_noinstr();
+	u64 time_start = local_clock_noinstr();
+	unsigned int loop_count = 0;
+	u64 limit;
 
 	dev->poll_time_limit = false;
 
 	raw_local_irq_enable();
-	if (!current_set_polling_and_test()) {
-		unsigned int loop_count = 0;
-		u64 limit;
 
-		limit = cpuidle_poll_time(drv, dev);
+	limit = cpuidle_poll_time(drv, dev);
 
-		while (!need_resched()) {
-			cpu_relax();
-			if (loop_count++ < POLL_IDLE_RELAX_COUNT)
-				continue;
+	while (!need_resched()) {
+		cpu_relax();
+		if (loop_count++ < POLL_IDLE_RELAX_COUNT)
+			continue;
 
-			loop_count = 0;
-			if (local_clock_noinstr() - time_start > limit) {
-				dev->poll_time_limit = true;
-				break;
-			}
+		loop_count = 0;
+		if (local_clock_noinstr() - time_start > limit) {
+			dev->poll_time_limit = true;
+			break;
 		}
 	}
 	raw_local_irq_disable();
 
-	current_clr_polling();
-
 	return index;
 }
 
-- 
2.46.0