[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [RFC PATCH 21/24] ARM: vITS: handle INVALL command
On Tue, 6 Dec 2016, Dario Faggioli wrote: > On Tue, 2016-12-06 at 13:53 -0800, Stefano Stabellini wrote: > > On Tue, 6 Dec 2016, Dario Faggioli wrote: > > > Sorry if I can't be more useful than this for now. :-/ > > > > We don't need scheduler support to implement interrupt migration. The > > question was much simpler than that: moving a vCPU with interrupts > > assigned to it is slower than moving a vCPU without interrupts > > assigned > > to it. You could say that the slowness is directly proportional do > > the > > number of interrupts assigned to the vCPU. Does the scheduler know > > that? > > Or blindly moves vCPUs around? Also see below. > > > Ah, ok, it is indeed a simpler question than I thought! :-) > > Answer: no, the scheduler does not use the information of how many or > what interrupts are being routed to a vCPU in any way. > > Just for the sake of correctness and precision, it does not "blindly > moves vCPUs around", as in, it follows some criteria for deciding > whether or not to move a vCPU, and if yes, where to, but among those > criteria, there is no trace of anything related to routed interrupts. > > Let me also add that the criteria are scheduler specific, so they're > different, e.g., between Credit and Credit2. > > Starting considering routed interrupt as a migration criteria in Credit > would be rather difficult. Credit use a 'best effort' approach for > migrating vCPUs, which is hard to augment. > > Starting considering routed interrupt as a migration criteria in > Credit2 would be much easier. Credit2's load balancer is specifically > designed for being extendible with things like that. It would require > some thinking, though, in order to figure out how important this > particular aspect would be, wrt others that are considered. > > E.g., if I have pCPU 0 loaded at 75% and pCPU 1 loaded at 25%, vCPU A > has a lot of routed interrupts, and moving it gives me perfect load > balancing (i.e., load will become 50% on pCPU 0 and 50% on pCPU 1) > should I move it or not? > Well, it depends if whether or not we think that the overhead we save > by not migrating outweights the benefit of a perfectly balanced system. Right. I don't know where to draw the line. I don't how much weight it should have, but certainly it shouldn't be considered the same thing as moving any other vCPU. _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx https://lists.xen.org/xen-devel
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