Messages in this thread | | | Date | Fri, 20 Apr 2018 15:42:45 +0100 | From | Quentin Perret <> | Subject | Re: [RFC PATCH v2 4/6] sched/fair: Introduce an energy estimation helper function |
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Hi Leo,
On Wednesday 18 Apr 2018 at 20:15:47 (+0800), Leo Yan wrote: > Sorry I introduce mess at here to spread my questions in several > replying, later will try to ask questions in one replying. Below are > more questions which it's good to bring up: > > The code for energy computation is quite neat and simple, but I think > the energy computation mixes two concepts for CPU util: one concept is > the estimated CPU util which is used to select CPU OPP in schedutil, > another concept is the raw CPU util according to CPU real running time; > for example, cpu_util_next() predicts CPU util but this value might be > much higher than cpu_util(), especially after enabled UTIL_EST feature > (I have shallow understanding for UTIL_EST so correct me as needed);
I'm not not sure to understand what you mean by higher than cpu_util() here ... In which case would that happen ?
cpu_util_next() is basically used to figure out what will be the cpu_util() of CPU A after task p has been enqueued on CPU B (no matter what A and B are).
> but this patch simply computes CPU capacity and energy with the single > one CPU utilization value (and it will be an inflated value afte enable > UTIL_EST). Is this purposed for simple implementation? > > IMHO, cpu_util_next() can be used to predict CPU capacity, on the other > hand, should we use the CPU util without UTIL_EST capping for 'sum_util', > this can be more reasonable to reflect the CPU utilization?
Why would a decayed utilisation be a better estimate of the time that a task is going to spend on a CPU ?
> > Furthermore, if we consider RT thread is running on CPU and connect with > 'schedutil' governor, the CPU will run at maximum frequency, but we > cannot say the CPU has 100% utilization. The RT thread case is not > handled in this patch.
Right, we don't account for RT tasks in the OPP prediction for now. Vincent's patches to have a util_avg for RT runqueues could help us do that I suppose ...
Thanks ! Quentin
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