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

["Chen, Tianyang" <tiche@seas.upenn.edu>]

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 The wiki will look a bit outdated for 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


_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xen.org
http://lists.xen.org/xen-devel