Re: [PATCH] [request for inclusion] Realtime LSM

Matt Mackall
2005-01-11T19:24:40Z

On Tue, Jan 11, 2005 at 08:05:08AM -0500, Paul Davis wrote:
> >> Running `nice --20' is still significantly worse than SCHED_FIFO, but
> >> not the unmitigated disaster shown in the middle column. But, this
> >> improved performance is still not adequate for audio work. The worst
> >> delay was absurdly long (~1/2 sec).
> >
> >Let's work on that. It'd be _far_ better to have unprivileged near-RT
> >capability everywhere without potential scheduling DoS.
>
> I am not sure what you mean here. I think we've established that
> SCHED_OTHER cannot be made adequate for realtime audio work. Its
> intended purpose (timesharing the machine in ways that should
> generally benefit tasks that don't do a lot and/or are dominated by
> user interaction, thus rendering the machine apparently responsive) is
> really at odds with what we need.

We have not established that at all. In principle, because SCHED_OTHER
tasks running at full priority lie on the boundary between SCHED_OTHER
and SCHED_FIFO, they can be made to run arbitrarily close to the
performance of tasks in SCHED_FIFO. With the upside that they won't be
able to deadlock the machine.

And I mean arbitrarily close in the strict delta-epsilon sense.
It's not perfect, but neither is SCHED_FIFO, in principle or in
practice.

--
Mathematics is the supreme nostalgia of our time.