linux-kernel - [PATCH] cpufreq/amd-pstate: Add comment explaining nominal

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Message-ID: <20260116214539.8139-1-juan.martinez@amd.com>
Date: Fri, 16 Jan 2026 15:45:39 -0600
From: Juan Martinez <juan.martinez@....com>
To: <Ray.Huang@....com>, <gautham.shenoy@....com>, <Mario.Limonciello@....com>
CC: <rafael@...nel.org>, <viresh.kumar@...aro.org>, <Perry.Yuan@....com>,
	<linux-pm@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<stable@...r.kernel.org>, <Juan.Martinez@....com>, <Kaushik.ReddyS@....com>,
	Juan Martinez <juan.martinez@....com>
Subject: [PATCH] cpufreq/amd-pstate: Add comment explaining nominal_perf usage for performance policy

Add comment explaining why nominal_perf is used for MinPerf when the
CPU frequency policy is set to CPUFREQ_POLICY_PERFORMANCE, rather than
using highest_perf or lowest_nonlinear_perf.

Signed-off-by: Juan Martinez <juan.martinez@....com>
---
 drivers/cpufreq/amd-pstate.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
index c45bc98721d2..88b26f36937b5 100644
--- a/drivers/cpufreq/amd-pstate.c
+++ b/drivers/cpufreq/amd-pstate.c
@@ -636,6 +636,19 @@ static void amd_pstate_update_min_max_limit(struct cpufreq_policy *policy)
 	WRITE_ONCE(cpudata->max_limit_freq, policy->max);
 
 	if (cpudata->policy == CPUFREQ_POLICY_PERFORMANCE) {
+		/*
+		 * For performance policy, set MinPerf to nominal_perf rather than
+		 * highest_perf or lowest_nonlinear_perf.
+		 *
+		 * Per commit 0c411b39e4f4c, using highest_perf was observed
+		 * to cause frequency throttling on power-limited platforms, leading to
+		 * performance regressions. Using lowest_nonlinear_perf would limit
+		 * performance too much for HPC workloads requiring high frequency
+		 * operation and minimal wakeup latency from idle states.
+		 *
+		 * nominal_perf therefore provides a balance by avoiding throttling
+		 * while still maintaining enough performance for HPC workloads.
+		 */
 		perf.min_limit_perf = min(perf.nominal_perf, perf.max_limit_perf);
 		WRITE_ONCE(cpudata->min_limit_freq, min(cpudata->nominal_freq, cpudata->max_limit_freq));
 	} else {