Re: [PATCH v2] xen/arm: implement GICD_I[S/C]ACTIVER reads

[George Dunlap <George.Dunlap@xxxxxxxxxx>]

> On Apr 3, 2020, at 9:47 AM, Marc Zyngier <maz@xxxxxxxxxx> wrote:
> 
> On 2020-04-02 19:52, Julien Grall wrote:
>> (+Marc)
> 
> Thanks for looping me in. Definitely an interesting read, but also a very
> puzzling one.

[snip]

> No. Low latency is a very desirable thing, but it doesn't matter at all when
> you don't even have functional correctness. To use my favourite car analogy,
> having a bigger engine doesn't help when you're about to hit the wall and
> have no breaks... You just hit the wall faster.

[snip]

> s/imprecise/massively incorrect/

[snip]

> There is just no way I'll ever accept a change to the GIC interrupt state
> machine for Linux. Feel free to try and convince other OS maintainers.

[snip]

> If I was someone developing a product using Xen/ARM, I'd be very worried
> about what you have written above. Because it really reads "we don't care
> about reliability as long as we can show amazing numbers". I really hope
> it isn't what you mean.

What's puzzling to me, is that what everyone else in this thread is that what 
Stefano is trying to do is to get Xen to be have like KVM.

Are they wrong?  If so, we can just do whatever Linux does.  If not, then you 
need to first turn all your imprecations about correctness, smashing into 
walls, concern for the sanity of maintainers and so on towards your own code 
first.

 -George