Re: [PATCH v3 0/2] KVM: ARM: Enable vtimers with user space gic

Andrew Jones
2016-09-19T07:52:22Z

On Fri, Sep 16, 2016 at 09:36:42PM +0200, Alexander Graf wrote:
>
>
> > Am 16.09.2016 um 15:46 schrieb Andrew Jones <drjones@redhat.com>:
> >
> >> On Fri, Sep 16, 2016 at 03:30:27PM +0200, Christoffer Dall wrote:
> >>> On Fri, Sep 16, 2016 at 02:31:42PM +0200, Paolo Bonzini wrote:
> >>>
> >>>
> >>> On 16/09/2016 14:30, Christoffer Dall wrote:
> >>>>>>> This patch set allows user space to receive vtimer events as well as mask
> >>>>>>> them, so that we can handle all vtimer related interrupt injection from user
> >>>>>>> space, enabling us to use architected timer with user space gic emulation.
> >>>>>>
> >>>>>> I have already voiced my concerns in the past, including face to face,
> >>>>>> and I'm going to repeat it: I not keen at all on adding a new userspace
> >>>>>> interface that is going to bitrot extremely quickly.
> >>>>>
> >>>>> You don't have automated tests set up? It's not going to bitrot if you
> >>>>> test it, either with kvm-unit-tests or just by smoke-testing Linux.
> >>>>> It's _for_ the raspi, but it's not limited to it.
> >>>>
> >>>> Our automated testing situation is not great, no. Something we're
> >>>> looking at, but have resource problems with.
> >>>
> >>> But it's not a good reason to hold back a feature...
> >>
> >> I didn't say that exactly, but choosing not to merge something we cannot
> >> maintain and which we're not paid to look after and where there's a
> >> minimal interest, is not entirely unreasonable.
> >>
> >> That being said, I'm not categorically against these patches, but I
> >> share Marc's view that we've already seen that non-vgic support had been
> >> broken for multiple versions without anyone complaining, and without
> >> automated testing or substantial interest in the work, the patches
> >> really are likely to bit-rot.
> >>
> >> But I haven't even looked at the patches in detail, I was just replying
> >> to the comment about testing.
> >
> > This may be a great time to start encouraging feature writers to submit
> > kvm-unit-tests patches at the same time as the feature (Hi Alex :-)
>
> I actually started off implementing this with the help of kvm-unit-tests. It's awesome!
>
> I'm lacking actual irq support to make the test reasonable though and wanted to get the kernel bits out first :). But I'll sit down on that again soon I hope.

I'm glad it looks like a good base for you. I need to get this series
https://github.com/rhdrjones/kvm-unit-tests/commits/arm/gic refreshed and
merged, and also it's time to start looking into adding interrupt
injection to chr-testdev. With those in place I hope it'll be an even
better base for you.

Thanks,
drew