* Balbir Singh <balbir@xxxxxxxxxxxxxxxxxx> wrote: > * Ingo Molnar <mingo@xxxxxxx> [2009-02-20 22:53:18]: > > > > > * Arjan van de Ven <arjan@xxxxxxxxxxxxx> wrote: > > > > > On Fri, 20 Feb 2009 17:07:37 +0100 > > > Ingo Molnar <mingo@xxxxxxx> wrote: > > > > > > > > > > > * Vaidyanathan Srinivasan <svaidy@xxxxxxxxxxxxxxxxxx> wrote: > > > > > > > > > > I'd also suggest to not do that rather ugly > > > > > > enable_timer_migration per-cpu variable, but simply reuse > > > > > > the existing nohz.load_balancer as a target CPU. > > > > > > > > > > This is a good idea to automatically bias the timers. But > > > > > this nohz.load_balancer is a very fast moving target and we > > > > > will need some heuristics to estimate overall system idleness > > > > > before moving the timers. > > > > > > > > > > I would agree that the power saving load balancer has a good > > > > > view of the system and can potentially guide the timer biasing > > > > > framework. > > > > > > > > Yeah, it's a fast moving target, but it already concentrates > > > > the load somewhat. > > > > > > > > > > I wonder if the real answer for this isn't to have timers be > > > considered schedulable-entities and have the regular scheduler > > > decide where they actually run. > > > > hm, not sure - it's a bit heavy for that. > > > > I think the basic timer migration policy should exist in user > space. I disagree. > One of the ways of looking at it is, as we begin to > consolidate, using range timers and migrating all timers to > lesser number of CPUs would make a whole lot of sense. > > As far as the scheduler making those decisions is concerned, > my concern is that the load balancing is a continuous process > and timers don't necessarily work that way. I'd put my neck > out and say that irqbalance, range timers and timer migration > should all belong to user space. irqbalance and range timers > do, so should timer migration. As i said it my first reply, IRQ migration is special because they are not kernel-internal objects, they come externally so there's a lot of user-space enumeration, policy and other steps involved. Furthermore, IRQs are migrated in a 'slow' fashion. Timers on the other hand are fast entities tied to _tasks_ primarily, not external entities. Hence they should migrate according to the CPU where the activities of the system concentrates - i.e. where tasks are running. Another thing: do you argue for the existing timer-migration code we have in mod_timer() to move to user-space too? It isnt a consistent argument to push 'some' of it to user-space, and some of it in kernel-space. Ingo _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
