Re: [PATCH] sched/fair: Prevent cpu_busy_time from exceeding actual_cpu_capacity

[Qais Yousef]

On 06/17/24 11:07, Vincent Guittot wrote:

> > And should effective_cpu_util() return a value higher than
> > get_actual_cpu_capacity()?
> 
> I don't think we should because we want to return the effective
> utilization not the actual compute capacity.
> Having an utilization of the cpu or group of cpus above the actual
> capacity or the original capacity mainly means that we will have to
> run longer
> 
> By capping the utilization we filter this information.
> 
> capacity orig = 800
> util_avg = 700
> 
> if we cap the capacity to 400 the cpu is expected to run twice longer
> for the same amount of work to be done

Okay makes sense. Wouldn't the util be 'wrong' (to what degree will depend on
min/max freq ratio) though?

We cap with arch_scale_capacity() still, I guess we know at this stage it is
100% wrong if we allow returning higher values?