Re: [PATCH RFC v1 1/4] rt: Add rt scheduler to hypervisor

[Andrew Cooper <andrew.cooper3@citrix.com>]

On 11/07/14 16:21, Dario Faggioli wrote:

>>>  #define XEN_SCHEDULER_CREDIT   5
>>>  #define XEN_SCHEDULER_CREDIT2  6
>>>  #define XEN_SCHEDULER_ARINC653 7
>>> +#define XEN_SCHEDULER_RT       8
>>> +
>>>  /* Set or get info? */
>>>  #define XEN_DOMCTL_SCHEDOP_putinfo 0
>>>  #define XEN_DOMCTL_SCHEDOP_getinfo 1
>>> @@ -367,6 +383,9 @@ struct xen_domctl_scheduler_op {
>>>          struct xen_domctl_sched_credit2 {
>>>              uint16_t weight;
>>>          } credit2;
>>> +        struct xen_domctl_sched_rt{
>>> +            XEN_GUEST_HANDLE_64(xen_domctl_sched_rt_params_t) schedule;
>>> +        } rt;
>>
>> Thinking more generally, is rt an appropriate name here?  It seems a
>> little generic, as there are several classes of realtime schedulers
>> employing different semantics and parameters.
>>
> That's true. The challenge here is finding a name which is
> representative enough of the specific characteristics of the scheduler,
> without it being known only in real-time research rooms! :-O
>
> I'd stick with sched_rt.c for the filename, as it's an implementation of
> EDF, after all, on top of which (read: in the same file) you can
> potentially implement a bunch of different scheduling algorithms and
> policies.
>
> This particular one is called "Deferrable Server" (DS). Since it's on
> top of EDF, which is a dynamic priority algorithm, it is sometimes
> called "Dynamic Deferrable Server" (DDS). It's also part of a class of
> algorithms known as "Resource Reservation" algorithms, which is how
> (well, one of the ways with which) the RT community refers to algos with
> a budgetting scheme inside it.
>
> So, ideas? RTDS (as per Real-Time Deferrable-Server)? RRESDS (Resource
> Reservation Deferrable Server)? Just DS (Deferrable Server)?
>
> I'm not sure I like much any of these...
>
> What was it that you had in mind when you said "there are several
> classes of realtime schedulers employing different semantics and
> parameters" ?
>
> Dario
>

Hmm - naming things is difficult.  How about bob?

My concern is that naming it "rt" seems too generic, and will cause
confusion of a) what type of realtime scheduler it is, and b) further
problems if someone wants to come and implement a different realtime
scheduler in the future.

XEN_SCHEDULER_RT_DS doesn't sound too bad.

~Andrew