linux-kernel - [PATCH] [PATCH] amd_pstate: fix erroneous highest

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Message-ID: <20240218161435.38312-2-lucasleeeeeeeee@gmail.com>
Date: Mon, 19 Feb 2024 00:10:31 +0800
From: Lucas Lee Jing Yi <lucasleeeeeeeee@...il.com>
To: rafael@...nel.org
Cc: Perry.Yuan@....com,
	Xiaojian.Du@....com,
	alexander.deucher@....com,
	bp@...en8.de,
	deepak.sharma@....com,
	li.meng@....com,
	linux-acpi@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-kselftest@...r.kernel.org,
	linux-pm@...r.kernel.org,
	mario.limonciello@....com,
	nathan.fontenot@....com,
	oleksandr@...alenko.name,
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	skhan@...uxfoundation.org,
	viresh.kumar@...aro.org,
	x86@...nel.org,
	Lucas Lee Jing Yi <lucasleeeeeeeee@...il.com>
Subject: [PATCH] [PATCH] amd_pstate: fix erroneous highest_perf value on some CPUs

On a Ryzen 7840HS the highest_perf value is 196, not 166 as AMD assumed.
This leads to the advertised max clock speed to only be 4.35ghz instead of 5.14ghz , leading to a large degradation in performance.

Fix the broken assumption and revert back to the old logic for getting highest_perf.

TEST:
Geekbench 6 Before Patch:
Single Core:	2325 (-22%)!
Multi Core:	11335 (-10%)

Geekbench 6 AFTER Patch:
Single Core:	2635
Multi Core:	12487

Signed-off-by: Lucas Lee Jing Yi <lucasleeeeeeeee@...il.com>
---
 drivers/cpufreq/amd-pstate.c | 22 ++++++++++------------
 1 file changed, 10 insertions(+), 12 deletions(-)

diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
index 08e112444c27..54df68773620 100644
--- a/drivers/cpufreq/amd-pstate.c
+++ b/drivers/cpufreq/amd-pstate.c
@@ -50,7 +50,6 @@
 
 #define AMD_PSTATE_TRANSITION_LATENCY	20000
 #define AMD_PSTATE_TRANSITION_DELAY	1000
-#define AMD_PSTATE_PREFCORE_THRESHOLD	166
 
 /*
  * TODO: We need more time to fine tune processors with shared memory solution
@@ -299,15 +298,12 @@ static int pstate_init_perf(struct amd_cpudata *cpudata)
 				     &cap1);
 	if (ret)
 		return ret;
-
-	/* For platforms that do not support the preferred core feature, the
-	 * highest_pef may be configured with 166 or 255, to avoid max frequency
-	 * calculated wrongly. we take the AMD_CPPC_HIGHEST_PERF(cap1) value as
-	 * the default max perf.
+ 
+	/* Some CPUs have different highest_perf from others, it is safer 
+	 * to read it than to assume some erroneous value, leading to performance issues.
 	 */
-	if (cpudata->hw_prefcore)
-		highest_perf = AMD_PSTATE_PREFCORE_THRESHOLD;
-	else
+	highest_perf = amd_get_highest_perf();
+	if(highest_perf > AMD_CPPC_HIGHEST_PERF(cap1))
 		highest_perf = AMD_CPPC_HIGHEST_PERF(cap1);
 
 	WRITE_ONCE(cpudata->highest_perf, highest_perf);
@@ -329,9 +325,11 @@ static int cppc_init_perf(struct amd_cpudata *cpudata)
 	if (ret)
 		return ret;
 
-	if (cpudata->hw_prefcore)
-		highest_perf = AMD_PSTATE_PREFCORE_THRESHOLD;
-	else
+	/* Some CPUs have different highest_perf from others, it is safer 
+	 * to read it than to assume some erroneous value, leading to performance issues.
+	 */
+	highest_perf = amd_get_highest_perf();
+	if(highest_perf > cppc_perf.highest_perf)
 		highest_perf = cppc_perf.highest_perf;
 
 	WRITE_ONCE(cpudata->highest_perf, highest_perf);
-- 
2.43.2