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

[Dario Faggioli <dario.faggioli@citrix.com>]

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On gio, 2014-09-04 at 10:47 -0400, Meng Xu wrote:

> 2014-09-04 10:27 GMT-04:00 George Dunlap
> <George.Dunlap@eu.citrix.com>:

>         
>         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.
> 

> 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.); 
>
Right.

> 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.
> 
xl builds on top of libxl. If, from libxl, setting and getting per-vcpu
values won't be possible, so it will be for xl.

I'd say printing just one set of params, the ones that applies to all
the vcpus of the domain is fine for 4.5. So, from xl, you'll get
something similar to this:

# xl sched-credit
Cpupool Pool-0: tslice=30ms ratelimit=1000us
Name                                ID Weight  Cap
Domain-0                             0    256    0

> 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 is the libxl API that has stability constraints, not xl sub-commands
output.

Of course, it's not very nice to turn something completely upside down.
But given the fact we're accepting the new scheduler as an experimental
feature, and the fact that `xl sched-rt' will be a new command being
introduced in 4.5, I don't think changing its output in 4.6 would be a
problem.

Regards,
Dario

-- 
<<This happens because I choose it to happen!>> (Raistlin Majere)
-----------------------------------------------------------------
Dario Faggioli, Ph.D, http://about.me/dario.faggioli
Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK)


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