cpufreq: Simplify freq limit handling

Drivers setting CPUFREQ_NEED_UPDATE_LIMITS expect target() to be invoked even if the target frequency remains unchanged, so they can update their internal policy limits state.

Currently the core invokes target() unconditionally whenever the requested frequency matches policy->cur for such drivers, even if policy->min and policy->max haven't changed since the previous update.

Track pending policy limit updates explicitly and skip redundant target() invocations when neither the target frequency nor the effective limits changed.

Signed-off-by Viresh Kumar <[email protected]>

Reviewed-by Lifeng Zheng <[email protected]>

---
  drivers/cpufreq/cpufreq.c | 31 ++++++++++++++++++++++---------
  include/linux/cpufreq.h   |  3 +++
  2 files changed, 25 insertions(+), 9 deletions(-)

drivers/cpufreq/cpufreq.c +22 -9

index 44eb1b7e7fc1..225228e9f4ed 100644
@@ -2366,9 +2366,13 @@ int __cpufreq_driver_target(struct cpufreq_policy *policy,
  	 * exactly same freq is called again and so we can save on few function
  	 * calls.
  	 */
-	if (target_freq == policy->cur &&
-	    !(cpufreq_driver->flags & CPUFREQ_NEED_UPDATE_LIMITS))
-		return 0;
+	if (target_freq == policy->cur) {
+		if (!(cpufreq_driver->flags & CPUFREQ_NEED_UPDATE_LIMITS) ||
+		    !policy->update_limits)
+			return 0;
+
+		policy->update_limits = false;
+	}
 
  	if (cpufreq_driver->target) {
  		/*

@@ -2620,6 +2624,7 @@ static int cpufreq_set_policy(struct cpufreq_policy *policy,
  {
  	struct cpufreq_policy_data new_data;
  	struct cpufreq_governor *old_gov;
+	unsigned int freq;
  	int ret;
 
  	memcpy(&new_data.cpuinfo, &policy->cpuinfo, sizeof(policy->cpuinfo));

@@ -2652,12 +2657,20 @@ static int cpufreq_set_policy(struct cpufreq_policy *policy,
  	 * compiler optimizations around them because they may be accessed
  	 * concurrently by cpufreq_driver_resolve_freq() during the update.
  	 */
-	WRITE_ONCE(policy->max, __resolve_freq(policy, new_data.max,
-					       new_data.min, new_data.max,
-					       CPUFREQ_RELATION_H));
-	new_data.min = __resolve_freq(policy, new_data.min, new_data.min,
-				      new_data.max, CPUFREQ_RELATION_L);
-	WRITE_ONCE(policy->min, new_data.min > policy->max ? policy->max : new_data.min);
+	freq = __resolve_freq(policy, new_data.max, new_data.min, new_data.max,
+			      CPUFREQ_RELATION_H);
+	if (freq != policy->max) {
+		WRITE_ONCE(policy->max, freq);
+		policy->update_limits = true;
+	}
+
+	freq = __resolve_freq(policy, new_data.min, new_data.min, new_data.max,
+			      CPUFREQ_RELATION_L);
+	freq = min(freq, policy->max);
+	if (freq != policy->min) {
+		WRITE_ONCE(policy->min, freq);
+		policy->update_limits = true;
+	}
 
  	trace_cpu_frequency_limits(policy);
 

include/linux/cpufreq.h +3 -0

index 4d4b4ed24b30..ae9d1ce4f49c 100644
@@ -146,6 +146,9 @@ struct cpufreq_policy {
  	/* Per policy boost supported flag. */
  	bool			boost_supported;
 
+	/* Pending policy->min/max update for the driver */
+	bool			update_limits;
+
  	 /* Cached frequency lookup from cpufreq_driver_resolve_freq. */
  	unsigned int cached_target_freq;
  	unsigned int cached_resolved_idx;

From: Lifeng Zheng <[email protected]>

cs_dbs_update() performs explicit checks against policy->min/max before updating the target frequency. These checks are redundant as __cpufreq_driver_target() already clamps the requested frequency to the valid policy limits.

Remove the unnecessary boundary checks and simplify the update logic.

This also fixes an issue introduced by commit 00bfe05889e9 ("cpufreq:
conservative: Decrease frequency faster for deferred updates"), where stale target comparisons could cause frequency updates to be skipped entirely after deferred adjustments.

Closes https://lore.kernel.org/all/[email protected]/ open here

Fixes 00bfe05889e9 ("cpufreq: conservative: Decrease frequency faster for deferred updates")

Signed-off-by Lifeng Zheng <[email protected]>

Co-developed-by Viresh Kumar <[email protected]>

Signed-off-by Viresh Kumar <[email protected]>

---
  drivers/cpufreq/cpufreq_conservative.c | 12 +-----------
  1 file changed, 1 insertion(+), 11 deletions(-)

drivers/cpufreq/cpufreq_conservative.c +1 -11

index df01d33993d8..0b32ae28ec85 100644
@@ -103,10 +103,6 @@ static unsigned int cs_dbs_update(struct cpufreq_policy *policy)
  	if (load > dbs_data->up_threshold) {
  		dbs_info->down_skip = 0;
 
-		/* if we are already at full speed then break out early */
-		if (requested_freq == policy->max)
-			goto out;
-
  		requested_freq += freq_step;
  		if (requested_freq > policy->max)
  			requested_freq = policy->max;

@@ -124,13 +120,7 @@ static unsigned int cs_dbs_update(struct cpufreq_policy *policy)
 
  	/* Check for frequency decrease */
  	if (load < cs_tuners->down_threshold) {
-		/*
-		 * if we cannot reduce the frequency anymore, break out early
-		 */
-		if (requested_freq == policy->min)
-			goto out;
-
-		if (requested_freq > freq_step)
+		if (requested_freq > policy->min + freq_step)
  			requested_freq -= freq_step;
  		else
  			requested_freq = policy->min;

Hello,

Here is the second version of this patchset.

V2:
- Add tags from reviewers.
- Drop intel-pstate change.

Lifeng Zheng (1):
cpufreq: conservative: Simplify frequency limit handling

Viresh Kumar (2):
cpufreq: Fix typo in comment
cpufreq: Avoid redundant target() calls for unchanged limits

 drivers/cpufreq/cpufreq.c              | 31 ++++++++++++++++++--------
 drivers/cpufreq/cpufreq_conservative.c | 12 +---------
 include/linux/cpufreq.h                |  5 ++++-
 3 files changed, 27 insertions(+), 21 deletions(-)

--

Hi,

Quoted 16 lines · Viresh Kumar

Hello,

Here is the second version of this patchset.

V2:
- Add tags from reviewers.
- Drop intel-pstate change.

Lifeng Zheng (1):
cpufreq: conservative: Simplify frequency limit handling

Viresh Kumar (2):
cpufreq: Fix typo in comment
cpufreq: Avoid redundant target() calls for unchanged limits

Quoted 6 lines

 drivers/cpufreq/cpufreq.c              | 31 ++++++++++++++++++--------
 drivers/cpufreq/cpufreq_conservative.c | 12 +---------
 include/linux/cpufreq.h                |  5 ++++-
 3 files changed, 27 insertions(+), 21 deletions(-)

--

All applied as 7.1-rc material, thanks!