Re: [PATCH v1 2/2] hw/mem/cxl_type3: allocate more vectors for MSI-X

[Hyeonggon Yoo]

On Tue, Nov 28, 2023 at 9:46 PM Jonathan Cameron
<Jonathan.Cameron@huawei.com> wrote:
>
> On Tue, 28 Nov 2023 09:27:28 +0900
> Hyeonggon Yoo <42.hyeyoo@gmail.com> wrote:
>
> > On Tue, Nov 28, 2023 at 2:53 AM Davidlohr Bueso <dave@stgolabs.net> wrote:
> > >
> > > On Mon, 27 Nov 2023, Hyeonggon Yoo wrote:
> > >
> > > >commit 43efb0bfad2b ("hw/cxl/mbox: Wire up interrupts for background
> > > >completion") enables notifying background command completion via MSI-X
> > > >interrupt (vector number 9).
> > > >
> > > >However, the commit uses vector number 9 but the maximum number of
> > > >entries is less thus resulting in error below. Fix it by passing
> > > >nentries = 10 when calling msix_init_exclusive_bar().
> > >
> > > Hmm yeah this was already set to 10 in Jonathan's tree, thanks for 
> > > reporting.
> >
> > Oh, yeah, it's based on the mainline tree. I should have checked Jonathan's.
> >
> > hmm it's already 10 there but vector number 9 is already being used by PCIe 
> > DOE.
> > So I think it should change msix_num = 11 and use vector number 10 for
> > background command completion interrupt instead?
> >
> > https://gitlab.com/jic23/qemu/-/commit/2823f19188664a6d48a965ea8170c9efa23cddab
>
> Whilst I clearly messed up a rebase as this wasn't intended, it should be fine
> to have multiple things sharing a vector.

I wasn't 100% sure of that, thanks for confirming.
I'll drop this patch in v2 (assuming it's going to be fixed in the
next PR of your tree)

For my own learning, I would like to give a few questions
(sorry to bother, no pressures):

> On my todo list is making the case of too few vectors being available work for
> all the cases in which case everything may end up on one vector.

You mean the device needs to support sharing
a vector for different features?

> So we do need to expand the vectors to cover what we are asking for, but
> moving this to 11 is a nice to have rather than required.

May I ask what do you mean by "expand the vectors" to cover what we
are asking for?

Thanks!
--
Hyeonggon