linux-kernel - [PATCH] cpuidle: don't wakeup processor when set a longer latency

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Date:	Wed, 8 May 2013 10:44:59 +0800
From:	Lianwei Wang <lianwei.wang@...il.com>
To:	linux-kernel@...r.kernel.org, linux-pm@...ts.linux-foundation.org
Subject: [PATCH] cpuidle: don't wakeup processor when set a longer latency

When a PM-Qos is updated, the cpuidle driver will wakeup all the CPUs
no matter what a latency is set. But actually it only need to wakeup
the CPUs when a shorter latency is set. In this way we can reduce the
cpu wakeup count and save battery.

So we can pass the prev_value to the notifier callback and check the
latency curr_value and prev_value in the cpuidle latency notifier
callback. It modify a common interface(dummy --> prev_value) but shall
be safe since no one use the dummy parameter currently.

diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c
index e1f6860..1e1758c 100644
--- a/drivers/cpuidle/cpuidle.c
+++ b/drivers/cpuidle/cpuidle.c
@@ -498,7 +498,11 @@ static void smp_callback(void *v)
 static int cpuidle_latency_notify(struct notifier_block *b,
                unsigned long l, void *v)
 {
-       smp_call_function(smp_callback, NULL, 1);
+       unsigned long prev_value = (unsigned long) v;
+
+       /* Dont't waktup processor when set a longer latency */
+       if (l < prev_value)
+               smp_call_function(smp_callback, NULL, 1);
        return NOTIFY_OK;
 }

diff --git a/kernel/power/qos.c b/kernel/power/qos.c
index 9322ff7..533b8bc 100644
--- a/kernel/power/qos.c
+++ b/kernel/power/qos.c
@@ -205,7 +205,7 @@ int pm_qos_update_target(struct pm_qos_constraints
*c, struct plist_node *node,
        if (prev_value != curr_value) {
                blocking_notifier_call_chain(c->notifiers,
                                             (unsigned long)curr_value,
-                                            NULL);
+                                            (void *)prev_value);
                return 1;
        } else {
                return 0;

Download attachment "0001-cpuidle-don-t-wakeup-processor-when-set-a-longer-lat.patch" of type "application/octet-stream" (1708 bytes)