linux/debian/patches/patchset-pf/amd-pstate/0020-cpufreq-amd-pstate-Set-the-initial-min_freq-to-lowes.patch

From f5b234be445a45b0bcacc37e0aad7a6bc7900eac Mon Sep 17 00:00:00 2001
From: Dhananjay Ugwekar <Dhananjay.Ugwekar@amd.com>
Date: Thu, 3 Oct 2024 08:39:54 +0000
Subject: cpufreq/amd-pstate: Set the initial min_freq to lowest_nonlinear_freq

According to the AMD architectural programmer's manual volume 2 [1], in
section "17.6.4.1 CPPC_CAPABILITY_1" lowest_nonlinear_perf is described
as "Reports the most energy efficient performance level (in terms of
performance per watt). Above this threshold, lower performance levels
generally result in increased energy efficiency. Reducing performance
below this threshold does not result in total energy savings for a given
computation, although it reduces instantaneous power consumption". So
lowest_nonlinear_perf is the most power efficient performance level, and
going below that would lead to a worse performance/watt.

Also, setting the minimum frequency to lowest_nonlinear_freq (instead of
lowest_freq) allows the CPU to idle at a higher frequency which leads
to more time being spent in a deeper idle state (as trivial idle tasks
are completed sooner). This has shown a power benefit in some systems,
in other systems, power consumption has increased but so has the
throughput/watt.

Use the get_init_min_freq() callback to set the initial lower limit for
amd-pstate driver to lowest_nonlinear_freq instead of lowest_freq.

Link: https://www.amd.com/content/dam/amd/en/documents/processor-tech-docs/programmer-references/24593.pdf [1]

Signed-off-by: Dhananjay Ugwekar <Dhananjay.Ugwekar@amd.com>
Reviewed-by: Mario Limonciello <mario.limonciello@amd.com>
---
 drivers/cpufreq/amd-pstate.c | 16 +++++++++-------
 1 file changed, 9 insertions(+), 7 deletions(-)

--- a/drivers/cpufreq/amd-pstate.c
+++ b/drivers/cpufreq/amd-pstate.c
@@ -1025,13 +1025,6 @@ static int amd_pstate_cpu_init(struct cp
 	if (cpu_feature_enabled(X86_FEATURE_CPPC))
 		policy->fast_switch_possible = true;
 
-	ret = freq_qos_add_request(&policy->constraints, &cpudata->req[0],
-				   FREQ_QOS_MIN, policy->cpuinfo.min_freq);
-	if (ret < 0) {
-		dev_err(dev, "Failed to add min-freq constraint (%d)\n", ret);
-		goto free_cpudata1;
-	}
-
 	ret = freq_qos_add_request(&policy->constraints, &cpudata->req[1],
 				   FREQ_QOS_MAX, policy->cpuinfo.max_freq);
 	if (ret < 0) {
@@ -1746,6 +1739,13 @@ static int amd_pstate_epp_resume(struct
 	return 0;
 }
 
+static int amd_pstate_get_init_min_freq(struct cpufreq_policy *policy)
+{
+	struct amd_cpudata *cpudata = policy->driver_data;
+
+	return READ_ONCE(cpudata->lowest_nonlinear_freq);
+}
+
 static struct cpufreq_driver amd_pstate_driver = {
 	.flags		= CPUFREQ_CONST_LOOPS | CPUFREQ_NEED_UPDATE_LIMITS,
 	.verify		= amd_pstate_verify,
@@ -1759,6 +1759,7 @@ static struct cpufreq_driver amd_pstate_
 	.update_limits	= amd_pstate_update_limits,
 	.name		= "amd-pstate",
 	.attr		= amd_pstate_attr,
+	.get_init_min_freq = amd_pstate_get_init_min_freq,
 };
 
 static struct cpufreq_driver amd_pstate_epp_driver = {
@@ -1775,6 +1776,7 @@ static struct cpufreq_driver amd_pstate_
 	.set_boost	= amd_pstate_set_boost,
 	.name		= "amd-pstate-epp",
 	.attr		= amd_pstate_epp_attr,
+	.get_init_min_freq = amd_pstate_get_init_min_freq,
 };
 
 static int __init amd_pstate_set_driver(int mode_idx)