Re: [Xen-devel] RTDS with extra time issue

[Andrii Anisov <andrii_anisov@xxxxxxxx>]

Hello Meng Xu,


Thank you for your explanation.

On 09.02.18 17:34, Meng Xu wrote:
> To make sure no deadline miss of a task on a VCPU, we must guarantee:
> 1) The VCPU gets its configured time, which is shown in your following 
> emails that it does;
> 2) When the VCPU ​gets its configured time, the task on the VCPU can 
> be scheduled. <-- This can be achieved by configuring the VCPU's 
> parameters correctly.
> The deadline miss problem in the test case you presented here is 
> likely caused by the case (2).
> Even if the DomR gets 5ms in every 10ms, the task (period  = 10ms, 
> budget = 4ms) on the VCPU will still  ​miss deadline.
> In theory, the domR  with period 10ms should be configured to have 
> budget = 7ms. But here the budget's configured to be 5ms, which is 
> less than the required.
> The foundamental reason is that the release time of RT task and the 
> task's VCPU is not synchronized.
> Here I show why we cannot assign the same/similar parameter of a task 
> to its VCPU. If you change the VCPU's budget to 5ms, the starvation 
> interval is 2 * ( period - budget) = 10ms, still making the VCPU's 
> task miss deadline.
> [Forgive me to attach a slide to explain this.]
I think I've got the point.

> If you want to keep the same VCPU parameter, can you try to set task's 
> period = 100ms and exe time = 40ms?
> By theory (I used CARTS to compute), a VCPU (10ms, 5ms) can schedule a 
> task (100ms, 40ms).
> Note that the resource demand of two RT tasks with the same 
> utilization is different: the task with smaller period has larger demand.
I'll do more experiments.

--

*Andrii Anisov*



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