Messages in this thread | | | From | Wei Wang <> | Date | Fri, 24 Jan 2020 12:55:55 -0800 | Subject | Re: [PATCH] [RFC] sched: restrict iowait boost for boosted task only |
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On Fri, Jan 24, 2020 at 3:30 AM Qais Yousef <qais.yousef@arm.com> wrote: > > On 01/24/20 11:01, Valentin Schneider wrote: > > On 24/01/2020 09:51, Quentin Perret wrote: > > >>> +static inline bool iowait_boosted(struct task_struct *p) > > >>> +{ > > >>> + return p->in_iowait && uclamp_eff_value(p, UCLAMP_MIN) > 0; > > >> > > >> I think this is overloading the usage of util clamp. You're basically using > > >> cpu.uclamp.min to temporarily switch iowait boost on/off. > > >> > > >> Isn't it better to add a new cgroup attribute to toggle this feature? > > >> > > >> The problem does seem generic enough and could benefit other battery-powered > > >> devices outside of the Android world. I don't think the dependency on uclamp && > > >> energy model are necessary to solve this. > > > > > > I think using uclamp is not a bad idea here, but perhaps we could do > > > things differently. As of today the iowait boost escapes the clamping > > > mechanism, so one option would be to change that. That would let us set > > > a low max clamp in the 'background' cgroup, which in turns would limit > > > the frequency request for those tasks even if they're IO-intensive. > > > > > > > So I'm pretty sure we *do* want tasks with the default clamps to get iowait > > boost'd. What we don't want are background tasks driving up the frequency, > > and that should be via uclamp.max (as Quentin is suggesting) rather than > > uclamp.min (as is suggested in the patch). > > > > Now, whether that is overloading the usage of uclamp... I'm not sure. > > One of the argument for uclamp was actually frequency selection, so if > > we just make iowait boost respect that, IOW not boost further than > > uclamp.max (which is a bit better than a simple on/off switch), that > > wouldn't be too crazy I think. > > Capping iowait boost value in schedutil based on uclamp makes sense indeed. > > What didn't make sense to me is the use of uclamp as a switch to toggle iowait > boost on/off. > > Cheers > > -- > Qais Yousef
Sounds like we all agree on adding a new toggle, so will move forward with that then. For capping iowait boost, it should be a seperate patch. I am not sure if we want to apply what's the current max clamp on the rq but I do see the per-task iowait boost makes sense.
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