Re: [Xen-devel] [PATCH v8]xen: sched: convert RTDS from time to event driven model

[Meng Xu <mengxu@xxxxxxxxxxxxx>]

On Sat, Mar 12, 2016 at 5:21 PM, Chen, Tianyang <tiche@xxxxxxxxxxxxxx> wrote:
>
>
> On 03/11/2016 11:54 PM, Meng Xu wrote:
>>
>> I'm focusing on the style and the logic in the replenish handler:
>>
>>>   /*
>>> @@ -160,6 +180,7 @@ struct rt_private {
>>>    */
>>>   struct rt_vcpu {
>>>       struct list_head q_elem;    /* on the runq/depletedq list */
>>> +    struct list_head replq_elem;/* on the repl event list */
>>
>>
>> missing space before /*
>>
>
> I wasn't sure if all the comments should be lined up or not. Maybe there
> should be one more space for all the fields so they nicely line up?
>
>>> +static int
>>> +deadline_queue_insert(struct rt_vcpu * (*_get_q_elem)(struct list_head
>>> *elem),
>>> +    struct rt_vcpu *svc, struct list_head *elem, struct list_head
>>> *queue)
>>> +{
>>> +    struct list_head *iter;
>>> +    int pos = 0;
>>> +
>>> +    list_for_each(iter, queue)
>>
>>
>> space after ( and before )
>> If not sure about the space, we can refer to the sched_credit.c for
>> the style as well, beside the CODING_STYLE file. :-)
>>
>
> Ok. But in __runq_pick() there is no space. Also there is no space in the
> definition of this macro:
> #define list_for_each(pos, head) \
> Which one should I follow?

It should have space before (. Some of the style in the old files may
not be correctly updated. :-( But when we introduce new code, we'd
better follow the rules....

>
>> One more thing we should think about is:
>> How can we "prove/test" the correctness of the scheduler?
>> Can we use xentrace to record the scheduling trace and then write a
>> userspace program to check the scheduling trace is obeying the
>> priority rules of the scheduler.
>>
> Thanks for the review Meng, I am still exploring xentrace and it can output
> scheduling events such as which vcpu is running on a pcpu. I think it's
> possible for the userspace program to check RTDS, based on cur_budget and
> cur_deadline. We need to have a very clear outline of rules, for the things
> we are concerned about. When you say correctness, what does it include? I'm
> thinking about rules for when a vcpu should preempt, tickle and actually be
> picked.

What you said should be included...
What's in my mind is checking the invariants in the EDF scheduling policy.
For example, at any time, the running VCPUs should have higher
priority than the VCPUs in runq;
At any time, the runq and replenish queue should be sorted based on EDF policy.

Meng

-- 
Meng Xu
PhD Student in Computer and Information Science
University of Pennsylvania
http://www.cis.upenn.edu/~mengxu/

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