Re: RT patch acceptance

Thomas Gleixner
2005-06-01T21:00:00Z

On Wed, 2005-06-01 at 21:22 +0200, Andrea Arcangeli wrote:
> On Wed, Jun 01, 2005 at 07:53:11PM +0200, Thomas Gleixner wrote:
> > Thank god thats not the case. We did a patent research on this last year
> > and the result was that you can replace the cli/sti by a software flag
> > in the OS itself without violating the patent.
>
> Did you publish something about it (so that people won't have to do it
> over and over again)?

I have no permission from the customer who actually payed the survey to
publish the results yet. But I continue asking for it.

> > The combination of replacing it in the host OS and running said host OS
> > as an idle task of the underlying RTOS would violate the patent.
> >
> > So if PREEMPT-RT would use a soft cli/sti emulation, no problem should
> > arise.
>
> So I wonder why it doesn't do that and it leaves local_irq_disable
> uncovered making it a "metal hard" instead of "ruby hard" like rtai.

I have a slightly outdated patch with that around on top of RT, but it
introduces yet another level of ugliness.
You must carefully identify the places where you really need the
hard_local_irq_dis/enable(). It's not hard though.

I used it in the early days of PREEMPT_RT to identify the IRQ off
sections and some other deadlocking scenarios. I kept this always as an
option for adding on top of Ingos implementation to close the gap to
"ruby".

tglx