Messages in this thread | | | Date | Mon, 8 Jul 2019 12:09:04 +0100 | From | Patrick Bellasi <> | Subject | Re: [RFC PATCH v2 0/5] sched/cpufreq: Make schedutil energy aware |
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On 03-Jul 17:36, Douglas Raillard wrote: > On 7/2/19 4:51 PM, Peter Zijlstra wrote: > > On Thu, Jun 27, 2019 at 06:15:58PM +0100, Douglas RAILLARD wrote:
[...]
> > I'm not immediately seeing how it is transient; that is, PELT has a > > wobble in it's steady state, is that accounted for? > > > > The transient-ness of the ramp boost I'm introducing comes from the fact that for a > periodic task at steady state, task_ue.enqueued <= task_u when the task is executing. ^^^^^^^^^^^^^^^
I find your above "at steady state" a bit confusing.
The condition "task_ue.enqueue <= task_u" is true only for the first task's big activation after a series of small activations, e.g. a task switching from 20% to 70%.
That's the transient stat you refer to, isn't it?
> That is because task_ue.enqueued is sampled at dequeue time, precisely at the moment > at which task_u is reaching its max for that task.
Right, so in the example above we will have enqueued=20% while task_u is going above to converge towards 70%
> Since we only take into account positive boosts, ramp boost will > only have an impact in the "increase transients".
Right.
I think Peter was referring to the smallish wobbles we see when the task already converged to 70%. If that's the case I would say they are already fully covered also by the current util_est.
You are also correct in pointing out that in the steady state ramp_boost will not be triggered in that steady state.
IMU, that's for two main reasons: a) it's very likely that enqueued <= util_avg b) even in case enqueued should turn out to be _slightly_ bigger then util_avg, the corresponding (proportional) ramp_boost would be so tiny to not have any noticeable effect on OPP selection.
Am I correct on point b) above?
Could you maybe come up with some experimental numbers related to that case specifically?
Best, Patrick
-- #include <best/regards.h>
Patrick Bellasi
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