Re: [Xen-devel] [PATCH v1 1/4] xen: add real time scheduler rt

[Meng Xu <xumengpanda@xxxxxxxxx>]

2014-09-03 12:06 GMT-04:00 George Dunlap <George.Dunlap@xxxxxxxxxxxxx>:

On Wed, Sep 3, 2014 at 4:13 PM, Meng Xu <xumengpanda@xxxxxxxxx> wrote:
> Hi George,
>
>
> 2014-09-03 10:20 GMT-04:00 George Dunlap <George.Dunlap@xxxxxxxxxxxxx>:
>
>> On Sun, Aug 24, 2014 at 11:58 PM, Meng Xu <mengxu@xxxxxxxxxxxxx> wrote:
>> > diff --git a/xen/include/public/domctl.h b/xen/include/public/domctl.h
>> > index 5b11bbf..27d01c1 100644
>> > --- a/xen/include/public/domctl.h
>> > +++ b/xen/include/public/domctl.h
>> > @@ -339,6 +339,19 @@ struct xen_domctl_max_vcpus {
>> >Â typedef struct xen_domctl_max_vcpus xen_domctl_max_vcpus_t;
>> >Â DEFINE_XEN_GUEST_HANDLE(xen_domctl_max_vcpus_t);
>> >
>> > +/*
>> > + * This structure is used to pass to rt scheduler from a
>> > + * privileged domain to Xen
>> > + */
>> > +struct xen_domctl_sched_rt_params {
>> > +Â Â /* get vcpus' info */
>> > +Â Â uint64_t period; /* s_time_t type */
>> > +Â Â uint64_t budget;
>> > +Â Â uint16_t index;
>> > +Â Â uint16_t padding[3];
>>
>> Why the padding?
>>
>
> I did this because of Jan's comment "Also, you need to pad the structure to
> a multiple of 8 bytes, or
> its layout will differ between 32- and 64-bit (tool stack) callers." I think
> what he said make sense so I added the padding here. :-)
>
> Here is the link: http://marc.info/?l=xen-devel&m=140661680931179&w=2

Right. :-)Â I personally prefer to handle that by re-arranging the
elements rather than adding padding, unless absolutely necessary. In
this case that shouldn't be too hard, particularly once we pare the
interface down so we only have one interface (either all one vcpu at a
time, or all batched vcpus).

âI agree. When we settle down the interface, I will implement it. At that time, I will prefer to handle the layout by rearranging the elements unless it is necessary to pad it. â

âSo let's first settle down the approach of setting/getting vcpus, (either one vcpu at a time or all batched vcpus.)â

âWhat do you guys think about the approach of setting/getting vcpus? which approach do you prefer? Can we vote for it? (or maybe there exist some other ways to reach agreement? :-))â

âMeng

-----------
Meng Xu
PhD Student in Computer and Information Science
University of Pennsylvania

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