Messages in this thread | | | Date | Wed, 18 Jan 2023 16:17:31 +0000 | Subject | Re: [PATCH v3] sched/fair: unlink misfit task from cpu overutilized | From | Dietmar Eggemann <> |
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On 17/01/2023 16:38, Qais Yousef wrote: > On 01/16/23 09:07, Dietmar Eggemann wrote: > > [...] > >> Not sure if people get what `performance requirements` mean here? I know >> we want to use `performance` rather `bandwidth hint` to describe what >> uclamp is. So shouldn't we use `utilization but also uclamp`? > > We do have the uclamp doc now which explains this, no? I'm not keen on > utilization because it's an overloaded term. In the context of uclamp
And `performance` isn't ? ;-) True, the doc refers to uclamp as a `performance requirements`.
> - utilization _signal_ in the scheduler is used to indicate performance > requirements of a workload, no?
I was referring to:
4569 static inline int task_fits_cpu(struct task_struct *p, int cpu) 4570 { 4571 unsigned long uclamp_min = uclamp_eff_value(p, UCLAMP_MIN); 4572 unsigned long uclamp_max = uclamp_eff_value(p, UCLAMP_MAX); 4573 unsigned long util = task_util_est(p); 4574 /* 4575 * Return true only if the cpu fully fits the task requirements, 4576 * which include the utilization but also the performance. ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 4577 */ 4578 return (util_fits_cpu(util, uclamp_min, uclamp_max, cpu) > 0); 4579 }
So here we explicitly talk about `utilization` (util_avg/util_est) versus `uclamp (max/min)` and the latter is referred as `performance`. You're right, we shouldn't refer to `uclamp (min/max)` as `utilization` either.
In other places we use:
select_idle_capacity()
/* This CPU fits with all capacity and performance requirements */ ^^^^^^^^ ^^^^^^^^^^^^^^^^^^^^^^^^
`capacity` is probably equal `utilization`? and `performance requirements` stand for `uclamp (min/max)`.
/* Only the min performance (i.e. uclamp_min) doesn't fit */ ^^^^^^^^^^^^^^^ here we link `min performance` explicitly to `uclamp_min`.
/* Look for the CPU with highest performance capacity. ^^^^^^^^^^^^^^^^^^^^ I guess this stands for `cap_orig - thermal_load_avg()`
feec()
/* Both don't fit performance (i.e. uclamp_min) but best energy cpu has ^^^^^^^^^^^ ^^^^^^^^^^^^^^^ better performance. */ ^^^^^^ ^^^^^^^^^^^
Here I assume `better performance` stands for higher `cap_orig - thermal_pressure', not for `uclamp min or max`?
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IMHO, referring to `uclamp (min/max)` as `performance (min/max) hint/(requirement)` is fine as long as it's done consistently in comments and the alias is not used for other items.
> > Using 'uclamp hint' if you found it really confusing, is fine by me. But I'd > rather steer away from 'bandwidth' or 'utilization' when describing uclamp and > its intention. > > I like using performance requirements because it enforces what this hint > actually means.
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