Messages in this thread |  | | Subject | Re: [PATCH v2] sched: rt: Make RT capacity aware | From | Dietmar Eggemann <> | Date | Tue, 4 Feb 2020 18:23:15 +0100 |
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On 03/02/2020 20:03, Qais Yousef wrote: > On 02/03/20 13:12, Steven Rostedt wrote: >> On Mon, 3 Feb 2020 17:17:46 +0000 >> Qais Yousef <qais.yousef@arm.com> wrote:
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> In the light of strictly adhering to priority based scheduling; yes this makes > sense. Though I still think the migration will produce worse performance, but > I can appreciate even if that was true it breaks the strict priority rule. > >> >> You can add to the logic that you do not take over an RT task that is >> pinned and can't move itself. Perhaps that may be the only change to > > I get this. > >> cpu_find(), is that it will only pick a big CPU if little CPUs are >> available if the big CPU doesn't have a pinned RT task on it. > > But not that. Do you mind rephrasing it? > > Or let me try first: > > 1. Search all priority levels for a fitting CPU
Just so I get this right: All _lower_ prio levels than p->prio, right?
> 2. If failed, return the first lowest mask found > 3. If it succeeds, remove any CPU that has a pinned task in it > 4. If the lowest_mask is empty, return (2). > 5. Else return the lowest_mask with the fitting CPU(s)
Mapping this to the 5 FIFO tasks rt-tasks of Pavan's example (all p->prio=89 (dflt rt-app prio), dflt min_cap=1024 max_cap=1024) on a 4 big (Cpu Capacity=1024) 4 little (Cpu capacity < 1024) system:
You search from idx 1 to 11 [p->prio=89 eq. idx (task_pri)=12] and since there are no lower prior RT tasks the lowest mask of idx=1 (CFS or Idle) for the 5th RT task is returned.
But that means that CPU capacity trumps priority?
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