Re: [RFC PATCH 0/1] sched/pelt: Change PELT halflife at runtime

[Qais Yousef]

On 11/07/22 14:41, Peter Zijlstra wrote:
> On Thu, Sep 29, 2022 at 03:41:47PM +0100, Kajetan Puchalski wrote:
> 
> > Based on all the tests we've seen, jankbench or otherwise, the
> > improvement can mainly be attributed to the faster ramp up of frequency
> > caused by the shorter PELT window while using schedutil.
> 
> Would something terrible like the below help some?
> 
> If not, I suppose it could be modified to take the current state as
> history. But basically it runs a faster pelt sum along side the regular
> signal just for ramping up the frequency.

A bit of a tangent, but this reminded me of this old patch:

	https://lore.kernel.org/lkml/1623855954-6970-1-git-send-email-yt.chang@xxxxxxxxxxxx/

I think we have a bit too many moving cogs that might be creating undesired
compound effect.

Should we consider removing margins in favour of improving util ramp up/down?
(whether via util_est or pelt hf).

Only worry is lower end devices; but it seems to me better improve util
response and get rid of these magic numbers - if we can. Having the ability to
adjust them at runtime will help defer the trade-offs to sys admins.


Thanks

--
Qais Yousef