[PATCH v2 1/9] cpufreq/amd-pstate: Set min_limit_freq based on bios_min_perf

[K Prateek Nayak <kprateek.nayak@amd.com>]

amd_pstate_update_min_max_limit() sets the min_limit_perf to the
nominal_perf to avoid frequency throttling when the system is idling.

This was found to be an ideal default but is suboptimal for users who
have profiled their workload at different operating frequencies and have
configured the optimal idling frequency via bios_min_perf.

Use the bios_min_perf (if configured) as the min_limit_perf when running
with performance governor. In absence of bios_min_perf, continue using
nominal_perf as the default min_limit_perf to avoid throttling.

Fixes: 608a76b65288 ("cpufreq/amd-pstate: Add support for the "Requested CPU Min frequency" BIOS option")
Reviewed-by: Mario Limonciello (AMD) <superm1@kernel.org>
Signed-off-by: K Prateek Nayak <kprateek.nayak@amd.com>
---
Changelog rfc v1..v2:

o Picked up tag from Mario. (Thanks a ton!)
---
 drivers/cpufreq/amd-pstate.c | 21 +++++++++++++++------
 1 file changed, 15 insertions(+), 6 deletions(-)

diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
index b357189f4f8e..1157f05df10f 100644
--- a/drivers/cpufreq/amd-pstate.c
+++ b/drivers/cpufreq/amd-pstate.c
@@ -699,9 +699,12 @@ 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) {
+		u8 min_limit_perf = perf.bios_min_perf ?: perf.nominal_perf;
+		u32 min_limit_freq;
+
 		/*
-		 * For performance policy, set MinPerf to nominal_perf rather than
-		 * highest_perf or lowest_nonlinear_perf.
+		 * For performance policy, set MinPerf to nominal_perf / bios_min_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
@@ -709,11 +712,17 @@ static void amd_pstate_update_min_max_limit(struct cpufreq_policy *policy)
 		 * 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.
+		 * nominal_perf therefore provides a balanced default by avoiding
+		 * throttling while still maintaining enough performance for HPC
+		 * workloads when bios_min_perf is not available.
+		 *
+		 * When bios_min_perf is available, users have profiled their workloads
+		 * to understand the best idling frequency. Use that instead.
 		 */
-		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));
+		min_limit_freq = perf_to_freq(perf, cpudata->nominal_freq, min_limit_perf);
+		perf.min_limit_perf = min_limit_perf;
+
+		WRITE_ONCE(cpudata->min_limit_freq, min(min_limit_freq, cpudata->max_limit_freq));
 	} else {
 		perf.min_limit_perf = freq_to_perf(perf, cpudata->nominal_freq, policy->min);
 		WRITE_ONCE(cpudata->min_limit_freq, policy->min);
-- 
2.34.1