Patch "PM: EM: Fix inefficient states detection" has been added to the 5.14-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    PM: EM: Fix inefficient states detection

to the 5.14-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     pm-em-fix-inefficient-states-detection.patch
and it can be found in the queue-5.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 4e48d970f911a04df885a413d2f21a99f589e5c3
Author: Vincent Donnefort <vincent.donnefort@xxxxxxx>
Date:   Wed Sep 8 15:05:22 2021 +0100

    PM: EM: Fix inefficient states detection
    
    [ Upstream commit aa1a43262ad5df010768f69530fa179ff81651d3 ]
    
    Currently, a debug message is printed if an inefficient state is detected
    in the Energy Model. Unfortunately, it won't detect if the first state is
    inefficient or if two successive states are. Fix this behavior.
    
    Fixes: 27871f7a8a34 (PM: Introduce an Energy Model management framework)
    Signed-off-by: Vincent Donnefort <vincent.donnefort@xxxxxxx>
    Reviewed-by: Quentin Perret <qperret@xxxxxxxxxx>
    Reviewed-by: Lukasz Luba <lukasz.luba@xxxxxxx>
    Reviewed-by: Matthias Kaehlcke <mka@xxxxxxxxxxxx>
    Acked-by: Viresh Kumar <viresh.kumar@xxxxxxxxxx>
    Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/kernel/power/energy_model.c b/kernel/power/energy_model.c
index a332ccd829e24..97e62469a6b32 100644
--- a/kernel/power/energy_model.c
+++ b/kernel/power/energy_model.c
@@ -107,8 +107,7 @@ static void em_debug_remove_pd(struct device *dev) {}
 static int em_create_perf_table(struct device *dev, struct em_perf_domain *pd,
 				int nr_states, struct em_data_callback *cb)
 {
-	unsigned long opp_eff, prev_opp_eff = ULONG_MAX;
-	unsigned long power, freq, prev_freq = 0;
+	unsigned long power, freq, prev_freq = 0, prev_cost = ULONG_MAX;
 	struct em_perf_state *table;
 	int i, ret;
 	u64 fmax;
@@ -153,27 +152,21 @@ static int em_create_perf_table(struct device *dev, struct em_perf_domain *pd,
 
 		table[i].power = power;
 		table[i].frequency = prev_freq = freq;
-
-		/*
-		 * The hertz/watts efficiency ratio should decrease as the
-		 * frequency grows on sane platforms. But this isn't always
-		 * true in practice so warn the user if a higher OPP is more
-		 * power efficient than a lower one.
-		 */
-		opp_eff = freq / power;
-		if (opp_eff >= prev_opp_eff)
-			dev_dbg(dev, "EM: hertz/watts ratio non-monotonically decreasing: em_perf_state %d >= em_perf_state%d\n",
-					i, i - 1);
-		prev_opp_eff = opp_eff;
 	}
 
 	/* Compute the cost of each performance state. */
 	fmax = (u64) table[nr_states - 1].frequency;
-	for (i = 0; i < nr_states; i++) {
+	for (i = nr_states - 1; i >= 0; i--) {
 		unsigned long power_res = em_scale_power(table[i].power);
 
 		table[i].cost = div64_u64(fmax * power_res,
 					  table[i].frequency);
+		if (table[i].cost >= prev_cost) {
+			dev_dbg(dev, "EM: OPP:%lu is inefficient\n",
+				table[i].frequency);
+		} else {
+			prev_cost = table[i].cost;
+		}
 	}
 
 	pd->table = table;