Re: [RFC Patch 0/3] Putting the "Simple" back in sedf.

[Nate Studer <nate.studer@dornerworks.com>]

On 3/14/2014 3:22 PM, George Dunlap wrote:
> On 03/14/2014 07:13 PM, Nathan Studer wrote:
>> From: Nathan Studer <nate.studer@dornerworks.com>
>>
>> With the increased interest in embedded Xen, there is a need for a suitable
>> real-time scheduler.  The arinc653 scheduler currently only supports a
>> single core and has limited niche appeal, while the sedf scheduler is
>> widely consider deprecated and is currently a mess.
>>
>> Since both the CBS scheduler proposed by Dario and the schedulers of Xen-RT
>> use an edf scheduler as the lowest-level scheduling mechanism, it seems
>> worthwhile to start repurposing the sedf scheduler instead of creating a
>> completely new scheduler.
>>
>> This patchset begins this repurposing by removing the extra scheduling code
>> that has built up over the years, and returns the sedf scheduler to its
>> simple roots.
> 
> Hey Nate,
> 
> Thanks for these patches -- what you describe at a high level, making 
> sedf a suitable rts for embedded applications, sounds like a great idea.
> 
> I think what might be helpful in evaluating whether these patches are a 
> good idea at the high level is a bit of a description of where you see 
> this going long-term.  Can you sketch out, at a high level, what you 
> envision the sedf scheduler becoming?  What kinds of parameters and 
> features *will* it have?

In the long term, a more extensible version of Dario's favorite scheduler, CBS
(Constant Bandwidth Server):  a selectable budgeting algorithm that sets vcpu
deadlines with the sedf scheduler on the backend scheduling the vcpu with the
earliest deadline.  Preferably it would support other budgeting algorithms as
well such as Total Bandwidth Server, etc...

The parameters for the scheduler would be the budgeting algorithm, server
budget, and the server period.  The parameters for the domains/vcpus would be
domain/vcpu budget/timeslice and domain/vcpu period.

Those are our ideas though and I know that Dario and others have ideas as well,
so any feedback is appreciated.

In the short term, we are working on upstreaming a version of the CBS scheduler.
 Dario mentored Josh Whitehead, who works with me, in implementing a crude
version of it for his undergraduate project, so we are already half-way there.

http://wiki.xen.org/wiki/Archived/GSoC_2013#Temporal_Isolation_and_Multiprocessor_Support_in_the_SEDF_Scheduler

   Nate

> 
>   -George
>