Re: report a bug about sched_rt

Bill Gatliff
2009-07-27T13:35:22Z

Jamie Lokier wrote:
> Bill Gatliff wrote:
>
>> Jamie Lokier wrote:
>>
>>> I agree with communicting the desire explicitly to the scheduler.
>>>
>>> In the above example, the exact desire is "give me as much CPU as I
>>> ask for, because my hardware servicing will be adversely but
>>> non-fatally affected if you don't, and the amount of CPU needed to
>>> service the hardware cannot be determined in advance, but prevent me
>>>
>> >from blocking progress in the rest of the system by limiting my
>>
>>> exclusive ownership of the CPU".
>>>
>>> How do you propose to communicate that to the scheduler, if not by
>>> something rather like RT-bandwidth with downgrading to SCHED_OTHER
>>> when a policy limit is exceeded?
>>>
>> This is a great real-world problem. And there's no one-size-fits-all
>> answer, unfortunately.
>>
>> RT-bandwidth will give you the system behavior you are after, but it's a
>> pretty blunt instrument.
>>
>
> I'm under the impression that RT-bandwidth will *not* give the above
> system behaviour, and that is the whole reason for this thread.
>

I think I misspoke. What I meant to say is that RT-bandwidth will
(probably) prevent the hardware handler from eating 100% of the CPU.
But the system will suffer quite a, um, "discontinuity" when the
throttling happens.

>
>> I'd consider putting some throttling in your interrupt handler that
>> prevents it from running more than a certain amount of calculation per
>> interrupt event.
>>
>
> There is no interrupt handler in my specification above...
>

True. But in practice, I think such devices are typically
interrupt-driven at some level.

b.g.

--
Bill Gatliff
bgat@billgatliff.com