[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <Zv+rtIi5NMkWzayg@BLRRASHENOY1.amd.com>
Date: Fri, 4 Oct 2024 14:17:48 +0530
From: "Gautham R. Shenoy" <gautham.shenoy@....com>
To: Dhananjay Ugwekar <Dhananjay.Ugwekar@....com>
Cc: mario.limonciello@....com, perry.yuan@....com, ray.huang@....com,
rafael@...nel.org, viresh.kumar@...aro.org,
linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] cpufreq/amd-pstate: Set the initial min_freq to
lowest_nonlinear_freq
On Thu, Oct 03, 2024 at 08:39:54AM +0000, Dhananjay Ugwekar wrote:
> 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]
It is good enough to quote "AMD64 Architecture Programmer's Manual,
Volume 2, Revision 3.42" instead of providing a link.
Other than that,
Reviewed-by: Gautham R. Shenoy <gautham.shenoy@....com>
>
> Signed-off-by: Dhananjay Ugwekar <Dhananjay.Ugwekar@....com>
--
Thanks and Regards
gautham.
> ---
> drivers/cpufreq/amd-pstate.c | 16 +++++++++-------
> 1 file changed, 9 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
> index b7a17a3ef122..f8abae9a0156 100644
> --- a/drivers/cpufreq/amd-pstate.c
> +++ b/drivers/cpufreq/amd-pstate.c
> @@ -995,13 +995,6 @@ static int amd_pstate_cpu_init(struct cpufreq_policy *policy)
> 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) {
> @@ -1706,6 +1699,13 @@ static int amd_pstate_epp_resume(struct cpufreq_policy *policy)
> 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,
> @@ -1719,6 +1719,7 @@ static struct cpufreq_driver amd_pstate_driver = {
> .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 = {
> @@ -1735,6 +1736,7 @@ static struct cpufreq_driver amd_pstate_epp_driver = {
> .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)
> --
> 2.34.1
>
Powered by blists - more mailing lists