Re: [Xen-devel] Questions about the use of idle_vcpu[]

[Meng Xu <xumengpanda@xxxxxxxxx>]

Hi Dario,

On Mon, Jan 18, 2016 at 11:32 AM, Dario Faggioli
<dario.faggioli@xxxxxxxxxx> wrote:
> On Mon, 2016-01-18 at 11:07 -0500, Meng Xu wrote:
>> On Mon, Jan 18, 2016 at 6:00 AM, Dario Faggioli
>> <dario.faggioli@xxxxxxxxxx> wrote:
>> >
>> > RTDS behavior is broken in many respect, including this,
>> >
>> > and in fact,
>> > Meng and Tianyang are sending patches already to fix it (I'll let
>> > you
>> > guys have my comments shortly :-P).
>>
>>
>> Right. Tianyang and I are working on changing it from quantum driven
>> model to event-driven (or called timer-driven) model. Tianyang sent
>> out the first-version patch, but that version has some problems. He
>> is
>> working on the second version now.
>>
>> Hi Dario,
>> Tianyang is working on the second version right now.
>> If you could have a quick look at our discussion in that thread and
>> points out the "serious" issues in the decision, that will be great!
>>
> Ok, that's useful to know... I'll do that way.
>
>> We won't repeat the error again and again in the following versions.
>> As to the minor issues, we could refine it in the second version.
>> (I'm just thinking about how to save your time to have this done. For
>> the obvious things that I can handle, I will do it and avoid
>> "wasting"
>> you time. For the design choices that we are unclear, we definitely
>> need your insights/commands. ;-) )
>>
> Thanks for all this. :-)
>
>> Hi George,
>> Yes, you are right. The current RTDS should not return 0 when the
>> idle
>> VCPU is picked. I think it should do as what the credit does, i.e.,
>> returning a negative value to avoid arming the timer.
>> Right now, we are working on changing RTDS to event-driven model. We
>> will fix this in theNah, the rework you're doing is big enough, that this 
>> change can very well find its place in there.
>  next version of the patch.
>>
>> If needed, we can send out a separate patch to fix this specific
>> issue
>> (i.e. it should return negative value when idle vcpu is picked.) I'm
>> ok with either way. Which way do you guys prefer?
>>
> Nah, the rework you're doing is big enough, that this change can very
> well find its place in there.
>
> Doing it right now will need efforts on both our sides, only for the
> sake of putting something from "broken" to "just a little bit less
> broken" state, and I don't think that's worth. :-P
>

I see and got it.

BTW,
please let me know if I should "ack" the decision. If not, I will not
send this kind of email in the future to avoid spamming your email
folders. ;-)

Best,

Meng


-----------
Meng Xu
PhD Student in Computer and Information Science
University of Pennsylvania
http://www.cis.upenn.edu/~mengxu/

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