mbox series

[v2,0/2] cpufreq/amd-pstate: Set initial min_freq to lowest_nonlinear_freq

Message ID 20241016144639.135610-1-Dhananjay.Ugwekar@amd.com
Headers show
Series cpufreq/amd-pstate: Set initial min_freq to lowest_nonlinear_freq | expand

Message

Dhananjay Ugwekar Oct. 16, 2024, 2:46 p.m. UTC 
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.

Our objective here is to update the initial lower frequency limit to 
lowest_nonlinear_freq, while allowing the user to later update the lower 
limit to anywhere between lowest_freq to highest_freq for the platform.

So, set the policy->min to lowest_nonlinear_freq in the ->verify() 
callback, only if the original value is equal to FREQ_QOS_MIN_DEFAULT_VALUE
(i.e. 0). Merge the two identical verify functions while at it.

Link: https://www.amd.com/content/dam/amd/en/documents/processor-tech-docs/programmer-references/24593.pdf [1]

Changes from v1:
* Modify the initial min_freq from verify callback, instead of adding a
  new callback in cpufreq_driver struct. (Rafael)

v1 Link: https://lore.kernel.org/linux-pm/20241003083952.3186-1-Dhananjay.Ugwekar@amd.com/

Dhananjay Ugwekar (2):
  cpufreq/amd-pstate: Remove the redundant verify() function
  cpufreq/amd-pstate: Set the initial min_freq to lowest_nonlinear_freq

 drivers/cpufreq/amd-pstate.c | 27 ++++++++++++++++-----------
 1 file changed, 16 insertions(+), 11 deletions(-)

Comments

Gautham R. Shenoy Oct. 17, 2024, 3:47 a.m. UTC | #1 
Hello Dhananjay,

On Wed, Oct 16, 2024 at 02:46:40PM +0000, Dhananjay Ugwekar wrote:
> Merge the two verify() callback functions and rename the
> cpufreq_policy_data argument for better readability.

Thanks for cleaning this up.

Reviewed-by: Gautham R. Shenoy <gautham.shenoy@amd.com>

--
Thanks and Regards
gautham.

> 
> Signed-off-by: Dhananjay Ugwekar <Dhananjay.Ugwekar@amd.com>
> ---
>  drivers/cpufreq/amd-pstate.c | 15 ++++-----------
>  1 file changed, 4 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
> index b7a17a3ef122..fa16d72d6058 100644
> --- a/drivers/cpufreq/amd-pstate.c
> +++ b/drivers/cpufreq/amd-pstate.c
> @@ -527,10 +527,10 @@ static void amd_pstate_update(struct amd_cpudata *cpudata, u32 min_perf,
>  	cpufreq_cpu_put(policy);
>  }
>  
> -static int amd_pstate_verify(struct cpufreq_policy_data *policy)
> +static int amd_pstate_verify(struct cpufreq_policy_data *policy_data)
>  {
> -	cpufreq_verify_within_cpu_limits(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;
>  }
>  
> @@ -1661,13 +1661,6 @@ static int amd_pstate_epp_cpu_offline(struct cpufreq_policy *policy)
>  	return 0;
>  }
>  
> -static int amd_pstate_epp_verify_policy(struct cpufreq_policy_data *policy)
> -{
> -	cpufreq_verify_within_cpu_limits(policy);
> -	pr_debug("policy_max =%d, policy_min=%d\n", policy->max, policy->min);
> -	return 0;
> -}
> -
>  static int amd_pstate_epp_suspend(struct cpufreq_policy *policy)
>  {
>  	struct amd_cpudata *cpudata = policy->driver_data;
> @@ -1723,7 +1716,7 @@ static struct cpufreq_driver amd_pstate_driver = {
>  
>  static struct cpufreq_driver amd_pstate_epp_driver = {
>  	.flags		= CPUFREQ_CONST_LOOPS,
> -	.verify		= amd_pstate_epp_verify_policy,
> +	.verify		= amd_pstate_verify,
>  	.setpolicy	= amd_pstate_epp_set_policy,
>  	.init		= amd_pstate_epp_cpu_init,
>  	.exit		= amd_pstate_epp_cpu_exit,
> -- 
> 2.34.1
>