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

Alexander Graf
2016-09-19T11:45:49Z

On 19.09.16 09:52, Andrew Jones wrote:
> 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.

Awesome. Let me know when you're further ahead with the gic work then so
that we can actually trigger interrupts and measure irq latencies :).

Until then, I sent the simplistic version that I used for bringup to the
list.

Alex