From ba9f0c8ca71a1c44e35dd8d3221abda0bd4e465a Mon Sep 17 00:00:00 2001 From: Dhananjay Ugwekar Date: Thu, 17 Oct 2024 05:39:30 +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. Modify the initial policy_data->min set by cpufreq-core to lowest_nonlinear_freq, in the ->verify() callback. Also set the cpudata->req[0] to FREQ_QOS_MIN_DEFAULT_VALUE (i.e. 0), so that it also gets overriden by the check in verify function. Link: https://www.amd.com/content/dam/amd/en/documents/processor-tech-docs/programmer-references/24593.pdf [1] Signed-off-by: Dhananjay Ugwekar Reviewed-by: Mario Limonciello --- drivers/cpufreq/amd-pstate.c | 21 ++++++++++++++++++++- 1 file changed, 20 insertions(+), 1 deletion(-) --- a/drivers/cpufreq/amd-pstate.c +++ b/drivers/cpufreq/amd-pstate.c @@ -559,8 +559,27 @@ cpufreq_policy_put: static int amd_pstate_verify(struct cpufreq_policy_data *policy_data) { + /* + * Initialize lower frequency limit (i.e.policy->min) with + * lowest_nonlinear_frequency which is the most energy efficient + * frequency. Override the initial value set by cpufreq core and + * amd-pstate qos_requests. + */ + if (policy_data->min == FREQ_QOS_MIN_DEFAULT_VALUE) { + struct cpufreq_policy *policy = cpufreq_cpu_get(policy_data->cpu); + struct amd_cpudata *cpudata; + + if (!policy) + return -EINVAL; + + cpudata = policy->driver_data; + policy_data->min = cpudata->lowest_nonlinear_freq; + cpufreq_cpu_put(policy); + } + cpufreq_verify_within_cpu_limits(policy_data); pr_debug("policy_max =%d, policy_min=%d\n", policy_data->max, policy_data->min); + return 0; } @@ -1009,7 +1028,7 @@ static int amd_pstate_cpu_init(struct cp policy->fast_switch_possible = true; ret = freq_qos_add_request(&policy->constraints, &cpudata->req[0], - FREQ_QOS_MIN, policy->cpuinfo.min_freq); + FREQ_QOS_MIN, FREQ_QOS_MIN_DEFAULT_VALUE); if (ret < 0) { dev_err(dev, "Failed to add min-freq constraint (%d)\n", ret); goto free_cpudata1;