linux-kernel - [PATCH] cpuidle: ladder: Add per CPU PM QoS resume latency support

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Message-ID: <20171019233340.GA13902@intel.com>
Date:   Thu, 19 Oct 2017 16:33:55 -0700
From:   Ramesh Thomas <ramesh.thomas@...el.com>
To:     linux-kernel@...r.kernel.org
Cc:     linux-pm@...r.kernel.org, rafael.j.wysocki@...el.com,
        alex.shi@...aro.org, daniel.lezcano@...aro.org
Subject: [PATCH] cpuidle: ladder: Add per CPU PM QoS resume latency support

Individual CPUs may have special requirements to not enter
deep idle states. For example, a CPU running real time
applications would not want to enter deep idle states to
avoid latency impacts. At the same time other CPUs that
do not have such a requirement could allow deep idle
states to save power.

This was already implemented in the menu governor.
Implementing similar changes in the ladder governor which
gets selected when CONFIG_NO_HZ and CONFIG_NO_HZ_IDLE are not
set. Refer following commits for the menu governor changes.

commit 9908859acaa9 ("cpuidle/menu: add per CPU PM QoS resume
latency consideration")
commit 6dbf5cea05a7 ("cpuidle: menu: Avoid taking spinlock for
accessing QoS values")

Signed-off-by: Ramesh Thomas <ramesh.thomas@...el.com>
---
 drivers/cpuidle/governors/ladder.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/cpuidle/governors/ladder.c b/drivers/cpuidle/governors/ladder.c
index ce1a2ff..f7cfee7 100644
--- a/drivers/cpuidle/governors/ladder.c
+++ b/drivers/cpuidle/governors/ladder.c
@@ -17,6 +17,7 @@
 #include <linux/pm_qos.h>
 #include <linux/jiffies.h>
 #include <linux/tick.h>
+#include <linux/cpu.h>
 
 #include <asm/io.h>
 #include <linux/uaccess.h>
@@ -67,10 +68,16 @@ static int ladder_select_state(struct cpuidle_driver *drv,
 				struct cpuidle_device *dev)
 {
 	struct ladder_device *ldev = this_cpu_ptr(&ladder_devices);
+	struct device *device = get_cpu_device(dev->cpu);
 	struct ladder_device_state *last_state;
 	int last_residency, last_idx = ldev->last_state_idx;
 	int first_idx = drv->states[0].flags & CPUIDLE_FLAG_POLLING ? 1 : 0;
 	int latency_req = pm_qos_request(PM_QOS_CPU_DMA_LATENCY);
+	int resume_latency = dev_pm_qos_raw_read_value(device);
+
+	/* resume_latency is 0 means no restriction */
+	if (resume_latency && resume_latency < latency_req)
+		latency_req = resume_latency;
 
 	/* Special case when user has set very strict latency requirement */
 	if (unlikely(latency_req == 0)) {
-- 
2.7.4