> From: Nauman Rafique <nauman@xxxxxxxxxx> > Date: Thu, Nov 13, 2008 02:27:41PM -0800 > > On Thu, Nov 13, 2008 at 11:15 AM, Fabio Checconi <fchecconi@xxxxxxxxx> wrote: > >> How the proportional weight division is done among tasks is a property > >> of IO scheduler. cfq decides to use time slices according to priority > >> and bfq decides to use tokens. So probably we can't move this to common > >> elevator layer. > >> > > > > cfq and bfq are pretty similar in the concepts they adopt, and the pure > > time-based approach of cfq can be extended to arbitrary hierarchies. > > > > Even in bfq, when dealing with groups that generate only seeky traffic > > we don't try to be fair in the service domain, as it would decrease too > > much the aggregate throughput, but we fall back to a time-based approach. > > > > [ This is a design choice, but it does not depend on the algorithms, > > and of course can be changed... ] > > > > The two approaches can be mixed/unified, for example, using wf2q+ to > > schedule the slices, in the time domain, of cfq; the main remaining > > difference would be the ability of bfq to provide service-domain > > guarantees. > > Before going into the design of elevator level scheduler, we should > have some consensus on abandoning the two level approach. Infact, it > would be useful if we had Ryo and Satoshi jump into this discussion > and express their opinion. > You're right. I was only trying to give some design elements thinking that they could help in the evaluation of the two approaches, talking of the one I know better. ... > >> So at this point of time I think that probably porting BFQ's hierarchical > >> scheduling implementation to other IO schedulers might make sense. Thoughts? > >> > > > > IMO for cfq, given the similarities, this can be done without conceptual > > problems. How to do that for schedulers like as, noop or deadline, and > > if this is the best solution, is an interesting problem :) > > It might be a little too early to start patching things into other > schedulers. First, because we still don't have a common ground on the > exact approach for proportional bandwidth division. Second, if > somebody is using vanilla no-op, deadline or as, do they really care > about proportional division? If they did, they would probably be using > cfq already. So we can have something going for cfq first, and then we > can move to other schedulers. > Sorry for being unclear, I didn't want to start patching anything. In my opinion a hierarchical extension of as/deadline poses some interesting scheduling issues, and exploring them can help in making better decisions. _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/virtualization
