Re: [Xen-devel] [PATCH v1 2/5] xen: sched: null: don't assign down vcpus to pcpus

[Dario Faggioli <dfaggioli@xxxxxxxx>]

On Mon, 2019-07-15 at 17:06 +0100, George Dunlap wrote:
> On 8/25/18 1:21 AM, Dario Faggioli wrote:
> > If a pCPU has been/is being offlined, we don't want it to be
> > neither
> > assigned to any pCPU, nor in the wait list.
> 
> I take it the first `pCPU` should be `vCPU`?
> 
Indeed. :-)

> Also, English grammar agreement is funny: `neither` needs to agree
> with
> `nor`, but the two do *not* agree with the original verb.  That is,
> the
> sentence should say:
> 
> "...we want it to be neither assigned to pCPU, nor in the wait list".
> 
Yep, now that I see it, this rings a bell back from my high-school
English class! :-O

Sorry... and thanks. :-)

> Both here and in the comment.
>
And in patch 3 changelog too, I'm afraid. :-P

> 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" ?

Thanks and Regards
-- 
Dario Faggioli, Ph.D
http://about.me/dario.faggioli
Virtualization Software Engineer
SUSE Labs, SUSE https://www.suse.com/
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<<This happens because _I_ choose it to happen!>> (Raistlin Majere)

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