Messages in this thread | | | Date | Fri, 24 Jan 2020 11:30:51 +0000 | From | Qais Yousef <> | Subject | Re: [PATCH] [RFC] sched: restrict iowait boost for boosted task only |
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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
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