Re: xen 4.5.0 rtds scheduler perform poorly with 2vms

[Dario Faggioli <dario.faggioli@citrix.com>]

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On Sun, 2015-11-29 at 04:46 -0800, Yu-An(Victor) Chen wrote:
> So st_jobs_stats for the missed deadline jobs are:
> 
> trial #1 composed of 2 tasks: total tasks utilization rate = 1
> 
> (period, exe, deadline)=(21ms,12.023ms,21ms) -> miss all deadline
> (period, exe, deadline)=(100ms,37.985ms,100ms) -> no miss
> 
> trial #2 composed of 2 tasks: total tasks utilization rate = 1
> 
> (period, exe, deadline)=(68ms,40.685ms,68ms) -> miss all deadline
> (period, exe, deadline)=(70ms,28.118ms,70ms) -> no miss
> 
> trial #3 composed of 2 tasks: total tasks utilization rate = 1
> 
> (period, exe, deadline)=(16ms,11.613ms,16ms) -> miss all deadline
> (period, exe, deadline)=(46ms,12.612ms,46ms) -> no miss
> 
The point is: how did you come up with these numbers? What both me and
Meng are trying to say is that the budget(s) and period(s) of the
(vCPU's of a) VM and the budgets and periods of the task running inside
the VM must fulfill certain relationships, or schedulability is not
something you can even hope for! :-/

> I do notice that for within the task that misses deadline, the
> completion time get progressively longer, 
> for example: for trial #3, a snapshot of the task st_jobs_stats tells
> me that
> the completion time of the job is 79ms and then 87ms, and then 95ms
> 
That depends on how missing a deadline is handled and accounted for. I
don't recall how Litmus^RT does that.

> ok, I will look into the reference you provide, 
>
Highly recommended. You'll find there info about this relationship
necessary between vCPUs' and tasks' parameter we're talking about. :-)

> I just started my research in the rt fields, there is still a lot for
> me to learn.
>
:-D

Regards,
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)


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