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

[Matt Mackall <mpm@selenic.com>]

On Tue, Jan 11, 2005 at 12:47:07PM -0800, Chris Wright wrote:
> Guys, could we please bring this back to a useful discussion.  None of
> you have commented on whether the rlimits for priority are useful.  As I
> said before, I've no real problem with the module as it stands since it's
> tiny, quite contained, and does something people need.  But I agree it'd
> be better to find something that's workable as long term solution.

I almost like it. I don't like that it exposes the internal scheduler
priorities directly (-tiny in fact has options to change these!). So
perhaps some thought could be given to either stratifying it a bit
more (>2000 for SCHED_FIFO, >1000 for SCHED_RR, then SCHED_OTHER) or
separate limits for the different scheduling disciplines. 

Right now, you can make a good argument that SCHED_FIFO > SCHED_RR >
SCHED_OTHER from a privilege point of view, but that could change if
we add a pseudo-RT scheduling class of some sort. Similarly, adding a
discipline means adding an rlimit with the split approach, so that's
not very friendly either.

Another way:

0-20: normal nice values (inverted)
>20: privilege to set any RT priority

Limiting to below normal nice is a little weird and the offset to make
everything positive is weird as well. Above 20, any RT app can starve
SCHED_OTHER and it's less important to dole out fine-grained levels
here as these apps must be engineered to cooperate to some degree
anyway.

But I'm also still not convinced this policy can't be most flexibly
handled by a setuid helper together with the mlock rlimit.

-- 
Mathematics is the supreme nostalgia of our time.