Re: [RFC][PATCH v0.1 5/6] sched/topology: Allow .setpolicy() cpufreq drivers to enable EAS

[Christian Loehle <christian.loehle@arm.com>]

On 11/8/24 16:41, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> 
> Some cpufreq drivers, like intel_pstate, have built-in governors that
> are used instead of regular cpufreq governors, schedutil in particular,
> but they can work with EAS just fine, so allow EAS to be used with
> those drivers.
> 
> Also update the debug message printed when the cpufreq governor in
> use is not schedutil and the related comment, to better match the
> code after the change.
> 
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> ---
> 
> I'm not sure how much value there is in refusing to enable EAS without
> schedutil in general.  For instance, if there are no crossover points
> between the cost curves for different perf domains, EAS may as well be
> used with the performance and powersave governors AFAICS.
 
Agreed, but having no cross-over points or no DVFS at all should be the
only instances, right?
For plain (non-intel_pstate) powersave and performance we could replace
sugov_effective_cpu_perf()
that determines the OPP of the perf-domain by the OPP they will be
choosing, but for the rest?
Also there is the entire uclamp thing, not sure what the best
solution is there.
Will intel_pstate just always ignore it? Might be better then to
depend on !intel_pstate?

> ---
>  kernel/sched/topology.c |    6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> Index: linux-pm/kernel/sched/topology.c
> ===================================================================
> --- linux-pm.orig/kernel/sched/topology.c
> +++ linux-pm/kernel/sched/topology.c
> @@ -251,7 +251,7 @@ static bool sched_is_eas_possible(const
>  		return false;
>  	}
>  
> -	/* Do not attempt EAS if schedutil is not being used. */
> +	/* Do not attempt EAS with a cpufreq governor other than schedutil. */
>  	for_each_cpu(i, cpu_mask) {
>  		policy = cpufreq_cpu_get(i);
>  		if (!policy) {
> @@ -263,9 +263,9 @@ static bool sched_is_eas_possible(const
>  		}
>  		gov = policy->governor;
>  		cpufreq_cpu_put(policy);
> -		if (gov != &schedutil_gov) {
> +		if (gov && gov != &schedutil_gov) {
>  			if (sched_debug()) {
> -				pr_info("rd %*pbl: Checking EAS, schedutil is mandatory\n",
> +				pr_info("rd %*pbl: Checking EAS, cpufreq governor is not schedutil\n",
>  					cpumask_pr_args(cpu_mask));
>  			}
>  			return false;
> 
> 
> 
>