linux-kernel - [PATCH v3 01/17] cpufreq: Prepare timer flags for hierarchical timer pull model

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Date:   Tue, 25 Oct 2022 15:58:34 +0200
From:   Anna-Maria Behnsen <anna-maria@...utronix.de>
To:     linux-kernel@...r.kernel.org
Cc:     Peter Zijlstra <peterz@...radead.org>,
        John Stultz <john.stultz@...aro.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        linux-pm@...r.kernel.org, Arjan van de Ven <arjan@...radead.org>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Frederic Weisbecker <fweisbec@...il.com>,
        Rik van Riel <riel@...hat.com>,
        Anna-Maria Behnsen <anna-maria@...utronix.de>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Michael Ellerman <mpe@...erman.id.au>
Subject: [PATCH v3 01/17] cpufreq: Prepare timer flags for hierarchical timer pull model

Note: This is a proposal only. I was waiting on input how to change this
driver properly to use the already existing infrastructure. See therfore
the thread on linux-pm mailinglist:
https://lore.kernel.org/linux-pm/4c99f34b-40f1-e6cc-2669-7854b615b5fd@linutronix.de/

gpstates timer is the only timer using TIMER_PINNED and TIMER_DEFERRABLE
flag. When moving to hierarchical timer pull model, pinned and deferrable
timers are stored in separate bases.

To ensure gpstates timer always expires on the CPU where it is pinned to,
keep only TIMER_PINNED flag and drop TIMER_DEFERRABLE flag.

While at it, rewrite comment explaining the rule for timer expiry for the
next interval and fix whitespace damages.

Signed-off-by: Anna-Maria Behnsen <anna-maria@...utronix.de>
Cc: linux-pm@...r.kernel.org
Cc: Rafael J. Wysocki <rafael@...nel.org>
Cc: Viresh Kumar <viresh.kumar@...aro.org>
Cc: Michael Ellerman <mpe@...erman.id.au>
---
 drivers/cpufreq/powernv-cpufreq.c | 15 +++++++--------
 1 file changed, 7 insertions(+), 8 deletions(-)

diff --git a/drivers/cpufreq/powernv-cpufreq.c b/drivers/cpufreq/powernv-cpufreq.c
index fddbd1ea1635..08d6bd54539d 100644
--- a/drivers/cpufreq/powernv-cpufreq.c
+++ b/drivers/cpufreq/powernv-cpufreq.c
@@ -640,18 +640,18 @@ static inline int calc_global_pstate(unsigned int elapsed_time,
 		return highest_lpstate_idx + index_diff;
 }
 
-static inline void  queue_gpstate_timer(struct global_pstate_info *gpstates)
+static inline void queue_gpstate_timer(struct global_pstate_info *gpstates)
 {
 	unsigned int timer_interval;
 
 	/*
-	 * Setting up timer to fire after GPSTATE_TIMER_INTERVAL ms, But
-	 * if it exceeds MAX_RAMP_DOWN_TIME ms for ramp down time.
-	 * Set timer such that it fires exactly at MAX_RAMP_DOWN_TIME
-	 * seconds of ramp down time.
+	 * Timer should expire next time after GPSTATE_TIMER_INTERVAL. If
+	 * the resulting interval (elapsed time + interval) between last
+	 * and next timer expiry is greater than MAX_RAMP_DOWN_TIME, ensure
+	 * it is maximum MAX_RAMP_DOWN_TIME when queueing the next timer.
 	 */
 	if ((gpstates->elapsed_time + GPSTATE_TIMER_INTERVAL)
-	     > MAX_RAMP_DOWN_TIME)
+	    > MAX_RAMP_DOWN_TIME)
 		timer_interval = MAX_RAMP_DOWN_TIME - gpstates->elapsed_time;
 	else
 		timer_interval = GPSTATE_TIMER_INTERVAL;
@@ -865,8 +865,7 @@ static int powernv_cpufreq_cpu_init(struct cpufreq_policy *policy)
 
 	/* initialize timer */
 	gpstates->policy = policy;
-	timer_setup(&gpstates->timer, gpstate_timer_handler,
-		    TIMER_PINNED | TIMER_DEFERRABLE);
+	timer_setup(&gpstates->timer, gpstate_timer_handler, TIMER_PINNED);
 	gpstates->timer.expires = jiffies +
 				msecs_to_jiffies(GPSTATE_TIMER_INTERVAL);
 	spin_lock_init(&gpstates->gpstate_lock);
-- 
2.30.2