Re: [Xen-devel] [PATCH v10 09/25] x86: refactor psr: L3 CAT: set value: implement framework.

[Lars Kurth <lars.kurth.xen@xxxxxxxxx>]

> On 20 Apr 2017, at 14:21, Jan Beulich <jbeulich@xxxxxxxx> wrote:
> 
>>>> On 20.04.17 at 15:02, <lars.kurth.xen@xxxxxxxxx> wrote:
>>> On 20 Apr 2017, at 10:43, Jan Beulich <jbeulich@xxxxxxxx> wrote:
>>> 
>>>>>> On 20.04.17 at 04:14, <yi.y.sun@xxxxxxxxxxxxxxx> wrote:
>>>> On 17-04-19 03:00:29, Jan Beulich wrote:
>>>>>>>> On 19.04.17 at 10:22, <yi.y.sun@xxxxxxxxxxxxxxx> wrote:
>>>>>> On 17-04-18 05:46:43, Jan Beulich wrote:
>>>>>>>>>> On 18.04.17 at 12:55, <yi.y.sun@xxxxxxxxxxxxxxx> wrote:
>>>>>>>> I made a test patch based on v10 and attached it in mail. Could you 
>>>>>>>> please
>>>>>>>> help to check it? Thanks!
>>>>>>> 

[Item 1]

>>>>>>> This looks reasonable at the first glance, albeit I continue to be
>>>>>>> unconvinced that this is the only (reasonable) way of solving the
>>>> 
>>>> Do you have any other suggestion on this? Thanks!
>>> 
>>> I'm sorry, but no. I'm already spending _much_ more time on this
>>> series than I should be, considering its (afaic) relatively low
>>> priority. I really have to ask you to properly think through both
>>> the data layout and code structure, including considering
>>> alternatives especially in places where you can _anticipate_
>>> controversy.
>> 
>> Jan, can you confirm whether you are happy with the current proposal. You 
>> say "this looks reasonable at the first glance", but then go on to say that 
>> there may be other "reasonable ways" of solving the problem at hand.
>> 
>> This is not very concrete and hard to respond to from a contributors point 
>> of view: it would be good to establish whether a) the v10 proposal in this 
>> area is good enough, b) whether there are any concrete improvements to be 
>> made.

> I understand it's not very concrete, but please understand that with
> the over 100 patches wanting looking at right now it is simply
> impossible for me to give precise suggestions everywhere. I really
> have to be allowed to defer to the originator to come up with
> possible better mechanisms (or defend what there is by addressing
> questions raised),

Jan, I don't object to the principle of deferring issues to a contributor, for 
contributor to defend their viewpoint or to come up with a better mechanism. I 
just observed, that I could not make a lot of sense what you were looking for 
in this particular review. I am assuming that it would be even harder for Yi. 

> especially with - as said - the amount of time spent
> here already having been way higher than is justifiable.

And of course we have passed the 4.9 code freeze, so some of the pressure is 
off. At the same time I understand that because of the upcoming releases you 
need to focus on bug fixes, etc.

> Just go and
> compare v10 with one of the initial versions: Almost all of the data
> layout and code flow have fundamentally changed, mostly based on
> feedback I gave. I'm sorry for saying that, but to me this is an
> indication that things hadn't been thought through well in the design
> phase, i.e. before even submitting a first RFC.

That is good feedback which may contain some valuable lessons. Once we are 
through this (or maybe at the summit) it may be worthwhile to look at what has 
gone wrong and see how we can do better in future.

[Item 2]

>> You say please think through whether "you can _anticipate_ controversy", but 
>> at the same time you can't currently identify/think of any issues. That 
>> seems 
>> to suggest to me that maybe the proposal is good enough. Or that something 
>> is 
>> missing, which has not been articulated. Taking into account language 
>> barriers, more clarity would probably be helpful.
> 
> I've given criteria by which I have the gut feeling (but no more)
> that this isn't the right approach. I'm absolutely fine to be
> convinced that my gut feeling is wrong. That would require to
> simply answer the question I raised multiple times, and which was
> repeatedly "answered" by simply re-stating previously expressed
> facts.

I have not followed the full thread. But it seems that we have communications 
issue there. Normally this happens when expectations don't quite match and one 
party (in this case Yi) does not quite get what the other one is looking for. 
Maybe the best approach would be for Yi to get some of these things resolved 
during a short IRC conversation with you. I did see him and others resolve some 
previous issues more effectively on IRC. 

> If this reaction of mine is not acceptable, all I can do is refrain
> from further looking at this series. And Yi, I certainly apologize
> for perhaps not doing these reviews wholeheartedly, since -
> as also expressed before - I continue to not really view this as
> very important functionality.

As I said earlier, I stepped in, as I didn't really understand what was going 
on. I think this is a little clearer now. 

So to summarise: 

On item 1: it appears that you are looking for a some more justification why 
some of the changes were made, maybe with a rationale for some of the choices 
that were made. Given that this is quite a complex series which has diverged 
quite a lot from the design, the goal is to make it easier for either you (or 
someone else) to sanity check the proposal which on the face of things look OK. 
But you have some doubts and you can't easily check against the design as it is 
out-of-date.

On item 2: you think something may not be quite right, but you can't really 
decide until a couple of questions (not quite sure which, but I am sure Yi can 
locate them) are answered.

Let me know whether this is actually true. 

> Yet considering for how long some
> of the versions hadn't been looked at by anyone at all, the
> alternative would have been to simply let it sit further without
> looking at it. I actually take this lack of interest by others as an
> indication that I'm not the only one considering this nice to have,
> but no more.

That's a good point. There have been some comments from others, but it is also 
true that 66% of comments on this series did come from you (see 
https://xen.biterg.io:443/goto/72a753919aa8e3205d03da7b430d2696). On the other 
hand, this is also a series which is hard to hand over to someone else.

Regards
Lars



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