Re: Ichbiah 2022 compiler mode

[Niklas Holsti <niklas.holsti@tidorum.invalid>]

On 2024-09-14 9:13, Randy Brukardt wrote:
> "Niklas Holsti" <niklas.holsti@tidorum.invalid> wrote in message
> news:lkg1vvF1tp6U1@mid.individual.net...
> ...
>>> Priorities are just optimization on how to manage cores when there are
>>> not enough of them.
>>
>> In some contexts it could be optimization -- for example, to increase
>> throughput in a soft real-time system -- but in hard real-time systems
>> priorities (or deadlines) are needed for correctness, not just for
>> optimizatiion.
> 
> This I don't buy: priorities never help for correctness. At least not
> without extensive static analysis, but if you can do that, you almost
> certainly can do the correctness without depending upon priorities.


You misunderstood me; perhaps I was too brief.

I said "hard real-time systems", which means that the program is correct 
only if it meets its deadlines, for which priorities or deadline-based 
scheduling are necessary if there are fewer cores than 
concurrent/parallel activities, and the application has a wide range of 
deadlines and activity execution times.

(To be honest, there is the alternative of using a single thread that is 
manually sliced into small bits, interleaving all the activities 
increment by increment, according to a static, cyclic schedule, but that 
is IMO a horribly cumbersome and unmaintainable design, though 
unfortunately still required in some contexts.)

I believe we agree that priorities should be used for other things, such 
as controlling access to shared data, only if there is a well-defined 
and safe mechanism for it, such as protected objects with priority 
ceilings and priority inheritance on a single core.