Re: [Xen-devel] [PATCH v9]xen: sched: convert RTDS from time to event driven model

["Chen, Tianyang" <tiche@xxxxxxxxxxxxxx>]

On 03/16/2016 10:25 AM, Dario Faggioli wrote:
> Ok, it's about time that we deal with this changelog!
>
> On Mon, 2016-03-14 at 20:04 -0400, Tianyang Chen wrote:
> > Budget replenishment and enforcement are separated by adding
> > a replenishment timer, which fires at the next most imminent
> > release time of all runnable vcpus.
> First of all, state (quickly) the "problems". So, right now:
>   - the scheduler, although the algorithm is event driven by nature,
>     follow a time driven model (is invoked periodically!), making the
>     code looks unnatural;
>   - budget replenishment logic, budget enforcement logic and scheduling
>     decisions are mixed and entangled, making the code hard to
>     understand;
>   - the various queues of vcpus are scanned various times, making the
>     code inefficient;
>
> Then describe your solution. The first sentence you've got up above is
> ok...
>
> > A replenishment queue has been added to keep track of all vcpus that
> > are runnable.
> ...and this one too.
>
> > The following functions have major changes to manage the
> > replenishment
> > events and timer.
> >
> > repl_handler(): It is a timer handler which is re-programmed
> > to fire at the nearest vcpu deadline to replenish vcpus.
> >
> > rt_schedule(): picks the highest runnable vcpu based on cpu
> > affinity and ret.time will be passed to schedule(). If an idle
> > vcpu is picked, -1 is returned to avoid busy-waiting. repl_update()
> > has been removed.
> >
> > rt_vcpu_wake(): when a vcpu wakes up, it tickles instead of
> > picking one from the run queue.
> >
> > rt_context_saved(): when context switching is finished, the
> > preempted vcpu will be put back into the runq.
> This is too detailed for a changelog. If you want this information to
> live somewhere (it already lives in the list archives, actually), make
> a cover letter (this is just one patch, so it's not required, but
> nothing forbids that). Or put it in a wiki page. Or write a blog post.
> Or (which would be kind of nice) all of them! :-)
I was thinking about this as well. The wiki will look a bit outdated for 
RTDS if this patch goes through. Meng: Do you think we should put extra 
information in the wiki? Someone's gotta update it sooner or later.
Thanks for the review Dario. I will put everything together soon.

Tianyang


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