Re: [ANNOUNCE] Adeos nanokernel for Linux kernel

Peter Wächtler
2002-06-06T08:49:50Z

Daniel Phillips wrote:
> On Wednesday 05 June 2002 23:22, Oliver Xymoron wrote:
>
>>On Wed, 5 Jun 2002, Daniel Phillips wrote:
>>
>>
>
>>Worst case for this is devices
>>queues for disks. Go through the thought experiment of what happens when
>>an RT task and a !RT task interleave disk access. Worse, what happens when
>>they're creating files (and all the locking that entails) in the same
>>directory.
>>
>
> I mentioned somewhere that the realtime filesystem would get its own
> volume. That's a big help, because it means that the entire filesystem
> can run in the RTOS, and we only have to worry about the block queue,
> which is an interesting and tractable problem from the realtime point
> of view. Obviously, we want the RTOS to operate the block queue, and
> yes, we want it to be efficient.
>
> Our current block queue design would benefit a lot from the kind of
> thinking that would be required to make it realtime.
>
>

You know that spinning disks do some recalibrations?

Whatever marketing tries to imply with "realtime volumes" - the
technology only tries to make better promises (think of AV disks
for better sustained rate).

LynxOS (now LynuxWorks) has some patents for priority based IO.
And yes, I know about "resource kernels" and alike.
But that does not count for spinning disks: they are *not* predictable.
And think about the shared bus like PCI - out of *hard realtime* when
not talking about worst cases in ranges of seconds.