linux-kernel - [RFC v5 3/3] cpuidle-powernv : Recompute the idle-state timeouts when state usage is enabled/disabled

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Message-Id: <20191003062646.54258-4-huntbag@linux.vnet.ibm.com>
Date:   Thu,  3 Oct 2019 01:26:46 -0500
From:   Abhishek Goel <huntbag@...ux.vnet.ibm.com>
To:     linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org
Cc:     npiggin@...il.com, rjw@...ysocki.net, daniel.lezcano@...aro.org,
        mpe@...erman.id.au, ego@...ux.vnet.ibm.com, dja@...ens.net,
        Abhishek Goel <huntbag@...ux.vnet.ibm.com>
Subject: [RFC v5 3/3] cpuidle-powernv : Recompute the idle-state timeouts when state usage is enabled/disabled

The disable callback can be used to compute timeout for other states
whenever a state is enabled or disabled. We store the computed timeout
in "timeout" defined in cpuidle state strucure. So, we compute timeout
only when some state is enabled or disabled and not every time in the
fast idle path.
We also use the computed timeout to get timeout for snooze, thus getting
rid of get_snooze_timeout for snooze loop.

Signed-off-by: Abhishek Goel <huntbag@...ux.vnet.ibm.com>
---
 drivers/cpuidle/cpuidle-powernv.c | 35 +++++++++++--------------------
 include/linux/cpuidle.h           |  1 +
 2 files changed, 13 insertions(+), 23 deletions(-)

diff --git a/drivers/cpuidle/cpuidle-powernv.c b/drivers/cpuidle/cpuidle-powernv.c
index d7686ce6e..a75226f52 100644
--- a/drivers/cpuidle/cpuidle-powernv.c
+++ b/drivers/cpuidle/cpuidle-powernv.c
@@ -45,7 +45,6 @@ struct stop_psscr_table {
 static struct stop_psscr_table stop_psscr_table[CPUIDLE_STATE_MAX] __read_mostly;
 
 static u64 default_snooze_timeout __read_mostly;
-static bool snooze_timeout_en __read_mostly;
 
 static u64 forced_wakeup_timeout(struct cpuidle_device *dev,
 				 struct cpuidle_driver *drv,
@@ -67,26 +66,13 @@ static u64 forced_wakeup_timeout(struct cpuidle_device *dev,
 	return 0;
 }
 
-static u64 get_snooze_timeout(struct cpuidle_device *dev,
-			      struct cpuidle_driver *drv,
-			      int index)
+static void pnv_disable_callback(struct cpuidle_device *dev,
+				 struct cpuidle_driver *drv)
 {
 	int i;
 
-	if (unlikely(!snooze_timeout_en))
-		return default_snooze_timeout;
-
-	for (i = index + 1; i < drv->state_count; i++) {
-		struct cpuidle_state *s = &drv->states[i];
-		struct cpuidle_state_usage *su = &dev->states_usage[i];
-
-		if (s->disabled || su->disable)
-			continue;
-
-		return s->target_residency * tb_ticks_per_usec;
-	}
-
-	return default_snooze_timeout;
+	for (i = 0; i < drv->state_count; i++)
+		drv->states[i].timeout = forced_wakeup_timeout(dev, drv, i);
 }
 
 static int snooze_loop(struct cpuidle_device *dev,
@@ -94,16 +80,20 @@ static int snooze_loop(struct cpuidle_device *dev,
 			int index)
 {
 	u64 snooze_exit_time;
+	u64 snooze_timeout = drv->states[index].timeout;
+
+	if (!snooze_timeout)
+		snooze_timeout = default_snooze_timeout;
 
 	set_thread_flag(TIF_POLLING_NRFLAG);
 
 	local_irq_enable();
 
-	snooze_exit_time = get_tb() + get_snooze_timeout(dev, drv, index);
+	snooze_exit_time = get_tb() + snooze_timeout;
 	ppc64_runlatch_off();
 	HMT_very_low();
 	while (!need_resched()) {
-		if (likely(snooze_timeout_en) && get_tb() > snooze_exit_time) {
+		if (get_tb() > snooze_exit_time) {
 			/*
 			 * Task has not woken up but we are exiting the polling
 			 * loop anyway. Require a barrier after polling is
@@ -168,7 +158,7 @@ static int stop_loop(struct cpuidle_device *dev,
 	u64 timeout_tb;
 	bool forced_wakeup = false;
 
-	timeout_tb = forced_wakeup_timeout(dev, drv, index);
+	timeout_tb = drv->states[index].timeout;
 
 	if (timeout_tb) {
 		/* Ensure that the timeout is at least one microsecond
@@ -263,6 +253,7 @@ static int powernv_cpuidle_driver_init(void)
 	 */
 
 	drv->cpumask = (struct cpumask *)cpu_present_mask;
+	drv->disable_callback = pnv_disable_callback;
 
 	return 0;
 }
@@ -422,8 +413,6 @@ static int powernv_idle_probe(void)
 		/* Device tree can indicate more idle states */
 		max_idle_state = powernv_add_idle_states();
 		default_snooze_timeout = TICK_USEC * tb_ticks_per_usec;
-		if (max_idle_state > 1)
-			snooze_timeout_en = true;
  	} else
  		return -ENODEV;
 
diff --git a/include/linux/cpuidle.h b/include/linux/cpuidle.h
index 1729a497b..64195861b 100644
--- a/include/linux/cpuidle.h
+++ b/include/linux/cpuidle.h
@@ -50,6 +50,7 @@ struct cpuidle_state {
 	int		power_usage; /* in mW */
 	unsigned int	target_residency; /* in US */
 	bool		disabled; /* disabled on all CPUs */
+	unsigned long long timeout; /* timeout for exiting out of a state */
 
 	int (*enter)	(struct cpuidle_device *dev,
 			struct cpuidle_driver *drv,
-- 
2.17.1