Re: [PATCH v1 3/4] libxl: add rt scheduler

[George Dunlap <george.dunlap@eu.citrix.com>]

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On 09/04/2014 03:47 PM, Meng Xu wrote:
> Hi George,
>
>
> 2014-09-04 10:27 GMT-04:00 George Dunlap <George.Dunlap@eu.citrix.com 
> <mailto:George.Dunlap@eu.citrix.com>>:
>
>     On Wed, Sep 3, 2014 at 4:33 PM, George Dunlap
>     <George.Dunlap@eu.citrix.com <mailto:George.Dunlap@eu.citrix.com>>
>     wrote:
>     >
>     > While the domctl interface is not stable, the libxl interface *is*
>     > stable, so we definitely need to think carefully about what we want
>     > this to look like.
>     >
>     > Let me give that a think. :-)
>
>     OK, so we had a chat about this at our team meeting today, and here is
>     what we came up with.
>
>     The feature freeze for 4.5 is next Wednesday.
>
>     The core scheduler is in good enough shape to be checked in as an
>     "experimental" mode, so it would be really nice to be able to get this
>     checked in.
>
>     The DOMCTL interface isn't stable so we can change that if we need to;
>     however, the libxl interface *is* stable.
>
>     The current libxl scheduler parameter interface assumes one set of
>     parameters per domain; it's not yet setup for per-vcpu parameters.  It
>     is unlikely that we would be able to converge on a new interface by
>     next week.
>
>     So the suggestion was this: For the moment, use the existing libxl
>     interface on a per-domain basis.  Internally, this will set all vcpus
>     to the same values.  This will allow us to check in a useable version
>     of the scheduler for people to test and improve.  Then for 4.6 we can
>     start working on a suitable libxl interface for setting per-vcpu
>     scheduling parameters.
>
>     Dario / Ian, did I miss anything?
>
>     Meng / &c, does that sound reasonable?
>
>
> I have a question as to the user interface.
> For 4.5, we only allow users to set all vcpus to the same values (I'm 
> totally fine with it.);
> But how about the get function? When users issue the command "xl 
> sched-rt", how should we display the parameters of vcpus? We just give 
> the "period", "budget" and "#VCPU" for a domain? I'm fine with this 
> display for 4.5.
>
> However ,my concerns is: In 4.6, when we allow vcpus to have different 
> parameters and need to display every vcpu's parameters, how should we 
> display when users use command "xl sched-rt"? When vcpus have 
> different period and budget, we cannot display like what we did in 4.5 
> then. :-(
>
> It's just my thought, just in case we neglect it. :-)

I think the xl interface doesn't have quite the same consistency 
guarantees as the libxl interface.  For now, I think just make it print 
one budget / period for the domain; and we can change it later.

I'll ping Ian Jackson to make sure he's OK with that.

  -George

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