Re: [Xen-devel] [PATCH v2 for Xen 4.6 4/4] xl: enabling XL to set per-VCPU parameters of a domain for RTDS scheduler

[Chong Li <lichong659@xxxxxxxxx>]

On Tue, Jun 9, 2015 at 3:01 AM, Dario Faggioli
<dario.faggioli@xxxxxxxxxx> wrote:
> On Mon, 2015-06-08 at 16:18 -0500, Chong Li wrote:
>> On Mon, Jun 8, 2015 at 11:21 AM, Dario Faggioli
>> <dario.faggioli@xxxxxxxxxx> wrote:
>> > On Mon, 2015-05-25 at 19:11 -0500, Chong Li wrote:
>
>> > I appreciate just now that this probably affect other bits of the
>> > interface, as well as other interfaces, and I think we should handle it
>> > consistently...
>> >
>> > What do you think?
>> > For example (although this belong to patch 3's review) what
>> > libxl_domain_sched_params_get() does in the case I jus described?
>>
>> Here, "-o/--output" is used for the users who only do per-dom
>> settings. In those cases, "-o" is provided to show per-dom parameters,
>> and the output is just the same as what the old RTDS tool does.
>>
> Right, I saw that. And as far as xl is concerned, this is ok... I just
> do not like the name "-o/--output". I'd rather go with something like
> "-a/--all", or implement something like this:
>
>  # xl sched-rtds -d 2 -v all
>
> This is a perhaps a bit more difficult to implement (but not so much,
> unless I'm overlooking something), but I personally like it better,
> considering it's similar to the syntax we already have for `xl
> vcpu-pin'.

How about making

# xl sched-rtds -d vm1

output the per-dom parameters (of vm1), and meanwhile let

# xl sched-rtds -d vm1 -v all

output the per-vcpu parameters (of vm1).

So, in this way, all the "per-vcpu" commands need to consistently specify "-v".

>
>> When "-o" is set, libxl_domain_sched_params_get() and
>> sched_rtds_domain_get() (both two functions in libxl.c) are called.
>>
> OTOH, while in libxl, the thing is different. I mean, you can't assume
> that a specific libxl function would be called _only_ in the way and
> from the places where you're calling it in xl: other toolstack building
> on top of libxl can try to do things differently!
>
> So, IIRC, in patch 3 you are just not touching
> libxl_domain_sched_params_get(), nor sched_rtds_domain_get() and
> (perhaps in another patch) xc_sched_rtds_domain_get(). What I'm asking
> is, what does it mean "users who only do per-dom settings"? What happens
> if I, for instance, do a bunch of:
>
>  libxl_vcpu_sched_params_set(...)
>
> for various vcpus, each one with different parameters, and then call:
>
>  libxl_domain_sched_params_get(...)
>
> Have you tested this case? What's the output?

I described this use case in the cover letter.

"This command should only be used when all vcpus of a domain have the
same parameters, otherwise the output
is pointless. The period and budget shown in the output are equal to
the parameters of the first
VCPU of each domain."

Or, I think we can just output a warning message in this case.

>
> 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)

Thanks,
Chong

-- 
Chong Li
Department of Computer Science and Engineering
Washington University in St.louis

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