On Sun, 16 Oct 2016 21:40:59 +0200 Luca Abeni <[email protected]> wrote:
> On Mon, 10 Oct 2016 13:08:18 +0200 > Peter Zijlstra <[email protected]> wrote: > > > On Mon, Oct 10, 2016 at 12:15:58PM +0200, Peter Zijlstra wrote: > > > However, I think there's a third alternative. I have memories of a > > > paper from UNC (I'd have to dig through the site to see if I can > > > still find it) where they argue that for a hierarchical (G-)FIFO > > > you should use minimal concurrency, that is run the minimal number > > > of (v)cpu servers. > > > > > > This would mean we give a single CBS parameter and carve out the > > > minimal number (of max CBS) (v)cpu that fit in that. > > > > > > I'm just not sure how the random affinity crap works out for that, > > > if we have the (v)cpu servers migratable in the G-EDF and migrate > > > to whatever is demanded by the task at runtime it might work, but > > > who knows.. Analysis would be needed I think. > > > > Hurm,.. thinking slightly more on this, this ends up being a DL task > > with random affinity, which is problematic IIRC. > Yes, there currently is no existing schedulability analysis for > multi-processor EDF with random affinities (as far as I know) Correction: it looks like I was wrong, and the schedulability of multi-processor EDF with arbitrary affinities has already been analysed in A. Gujarati, F. Cerqueira, and B. Brandenburg, “Multiprocessor Real-Time Scheduling with Arbitrary Processor Affinities: From Practice to Theory”, Real- Time Systems, Volume 51, Issue 4, pp. 440–483. Springer Verlag, 2015 (see https://www.mpi-sws.org/~bbb/papers/). Thanks to Giuseppe Lipari for pointing me to this paper. So, having DL tasks with arbitrary affinities is not a big problem from the theoretical point of view... The only issue is that the utilisation-based admission test that is currently implemented in the kernel does not work (and given the complexity of the analysis I think it is better not to perform it in the kernel :) Luca > but I > think we can at least have a look at developing this kind of analysis. > Giuseppe, what do you think?
