On Tue, 2019-07-16 at 12:02 +0000, George Dunlap wrote: > > On Jul 16, 2019, at 11:50 AM, Dario Faggioli <faggi...@suse.com> > > On Mon, 2019-07-15 at 17:06 +0100, George Dunlap wrote: > > > On 8/25/18 1:21 AM, Dario Faggioli wrote: > > > > > > > The other thing is, from a "developmental purity" point of view, > > > I > > > think > > > this series technically has a regression in the middle: cpu > > > offline / > > > online stops working between patch 2 and patch 4. But I'm > > > inclined > > > in > > > this case not to worry too much. :-) > > > > > Well, the point is that offlining/onlining does not work before > > this > > series. System does not crash, but behavior is wrong, as offline > > vCPUs > > stay assigned to pCPUs (keeping them idle) while online vCPUs are > > "trapped" in the wait list, which is wrong. > > > > So that's why I don't think there's much value in being consistent > > with > > such behavior throughout the series... which I guess is why you > > said > > you "won't worry too much in this case” ? > > It’s definitely sub-optimal from a system point of view; but from a > guest point of view, it does (or should) function. Before this > series, if a guest offline and then online vcpus, they should come > back. > Well, yes, I guess they should. IAC, one of the main backing usecases for these fixes is when null is used as the scheduler of the Xen PV- SHIM. In that case, if I remember correctly, the L1 and L2 vCPUs are created offline, and then onlined dynamically. And they don't come up. :-)
Anyway... > In the middle of this series, once a vcpu is offlined, it can’t be > brought back up. (That is, if I’m reading it right.) > ...Yes, at that stage, things are working even less. But more important... > But I’m not expecting people to be doing bisections of that > particular functionality in this particular scheduler very much. I > think the “benefit” of avoiding a complicated re-write is well worth > the “cost” of having that particular bisection fail, on the off > chance that anyone tries it. > ...As we fully agree on this, let's move on Regards -- Dario Faggioli, Ph.D http://about.me/dario.faggioli Virtualization Software Engineer SUSE Labs, SUSE https://www.suse.com/ ------------------------------------------------------------------- <<This happens because _I_ choose it to happen!>> (Raistlin Majere)
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