On Thu, Mar 3, 2016 at 7:00 AM, Viresh Kumar [off-list ref] wrote:

On 02-03-16, 03:12, Rafael J. Wysocki wrote:

quoted

Index: linux-pm/drivers/cpufreq/cpufreq.c
===================================================================

--- linux-pm.orig/drivers/cpufreq/cpufreq.c
+++ linux-pm/drivers/cpufreq/cpufreq.c

@@ -1772,6 +1772,39 @@ EXPORT_SYMBOL(cpufreq_unregister_notifie
  *                              GOVERNORS                            *
  *********************************************************************/

+/**
+ * cpufreq_driver_fast_switch - Carry out a fast CPU frequency switch.
+ * @policy: cpufreq policy to switch the frequency for.
+ * @target_freq: New frequency to set (may be approximate).
+ * @relation: Relation to use for frequency selection.
+ *
+ * Carry out a fast frequency switch from interrupt context.
+ *
+ * This function must not be called if policy->fast_switch_possible is unset.
+ *
+ * Governors calling this function must guarantee that it will never be invoked
+ * twice in parallel for the same policy and that it will never be called in
+ * parallel with either ->target() or ->target_index() for the same policy.
+ *
+ * If CPUFREQ_ENTRY_INVALID is returned by the driver's ->fast_switch()
+ * callback, the hardware configuration must be preserved.
+ */
+void cpufreq_driver_fast_switch(struct cpufreq_policy *policy,
+                             unsigned int target_freq, unsigned int relation)
+{
+     unsigned int freq;
+
+     if (target_freq == policy->cur)

Maybe an unlikely() here ?

quoted

+             return;
+
+     freq = cpufreq_driver->fast_switch(policy, target_freq, relation);
+     if (freq != CPUFREQ_ENTRY_INVALID) {
+             policy->cur = freq;

Hmm.. What will happen to the code relying on the cpufreq-notifiers
now ?

It will have a problem.

For that code it's like the CPU changing the frequency and not telling
it (which is not unusual for that matter).

Thanks,
Rafael