Re: preempt rt in commercial use

[Nivedita Singhvi <niv@us.ibm.com>]

On 09/14/2010 07:49 AM, Jeff Angielski wrote:

>> Isn't any case where preempt-rt does not behave as hard reatlime a bug in
>> preempt-rt, that should be reported to this list and eventually fixed?
>
> That is a philosophical question for the preempt-rt maintainers.
>
> I *believe* that the design goal for the preempt rt code is to minimize
> kernel latency. It's not to make the kernel deterministic to support
> hard realtime.

Er, sort of, not quite.

The design goal of the real-time kernel is most certainly to make the
kernel more deterministic, to the extent we can in a general-purpose way.

Determinism = capping max latencies.

It's better to have all hundred iterations of an operation take
45us each than to have 95 iterations take 30us and 5 iterations
take 75us. You want to be able to say, "this operation will take
at _most_ 50us" and have that be as true as possible.

We sacrifice overall throughput (ave latency) for determinism
(low max latency).

Not sure if that's what you intended to say, but hope that helps.

thanks,
Nivedita