Re: [PATCH v5 6/7] sched/deadline: Deferrable dl server

[Daniel Bristot de Oliveira]

On 11/8/23 13:44, Peter Zijlstra wrote:
> Should we rather not cap the runtime, something like so?
> 
> Because the above also causes period drift, which we do not want.

like in the example I showed before:

- 3/10 reservation (30%).
- w=waiting
- r=running
- s=sleeping
- T=throttled
- fair server dispatched at 0, starvation from RT.


|wwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwww|rrrrrrrrrrrrrrrrrrrrrrrrrrrrrr|TTTTTTTTTT[...]TTTTTTTTTTT|rrrrrrrrrrrrrrrrrrrrrrrrrrrrrrr|TTTTTTT
|___________________________period 1_________________________________|_________period 2________________________[...]___________|___period 3____________________|[.... internal-period
0---------1---------2---------3---------4---------5---------6--------7--------8---------9----------10.......11.[...]16.........17........18........19........20|[.... < Real-time
---------------------------------------------------------------------+---------------------------------------------------------|
                                                                     |                                                         +new period

>From "real-world/wall clock" the internal period shift produces the
"zerolax" timeline. It runs 3 units of time before the 10's.

If one has a mix of DL and FIFO task, and want to enforce
a given response time to the fair server, they can reduce the
fair server period to achieve that.

-- Daniel