Re: [Xen-devel] [PATCH v8 for Xen 4.7 1/4] xen: enable per-VCPU parameter for RTDS

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 21.03.16 at 17:03, <lichong659@xxxxxxxxx> wrote:
> On Mon, Mar 21, 2016 at 10:49 AM, Jan Beulich <JBeulich@xxxxxxxx> wrote:
>>>>> On 21.03.16 at 16:18, <lichong659@xxxxxxxxx> wrote:
>>> On Mon, Mar 21, 2016 at 8:35 AM, Jan Beulich <JBeulich@xxxxxxxx> wrote:
>>>>>>> On 18.03.16 at 22:26, <lichong659@xxxxxxxxx> wrote:
>>>>> --- a/xen/include/public/domctl.h
>>>>> +++ b/xen/include/public/domctl.h
>>>>> @@ -338,24 +338,64 @@ DEFINE_XEN_GUEST_HANDLE(xen_domctl_max_vcpus_t);
>>>>>  #define XEN_SCHEDULER_ARINC653 7
>>>>>  #define XEN_SCHEDULER_RTDS     8
>>>>>
>>>>> -/* Set or get info? */
>>>>> +typedef struct xen_domctl_sched_credit {
>>>>> +    uint16_t weight;
>>>>> +    uint16_t cap;
>>>>> +} xen_domctl_sched_credit_t;
>>>>> +
>>>>> +typedef struct xen_domctl_sched_credit2 {
>>>>> +    uint16_t weight;
>>>>> +} xen_domctl_sched_credit2_t;
>>>>> +
>>>>> +typedef struct xen_domctl_sched_rtds {
>>>>> +    uint32_t period;
>>>>> +    uint32_t budget;
>>>>> +} xen_domctl_sched_rtds_t;
>>>>> +
>>>>> +typedef struct xen_domctl_schedparam_vcpu {
>>>>> +    union {
>>>>> +        xen_domctl_sched_credit_t credit;
>>>>> +        xen_domctl_sched_credit2_t credit2;
>>>>> +        xen_domctl_sched_rtds_t rtds;
>>>>> +    } u;
>>>>> +    uint32_t vcpuid;
>>>>> +    uint16_t padding[2];
>>>>
>>>> So why uint16_t[2] instead of just uint32_t? And what's the
>>>> padding needed for in the first place?
>>>
>>> You're right. It's better to use uint32_t, which pads (the struct) to
>>> the 64-bit boundary.
>>
>> Which doesn't answer the "why in the first place" part - I don't
>> see why structure size needs to be a multiple of 64 bits.
>>
> In this patch post,
> 
> http://lists.xen.org/archives/html/xen-devel/2015-07/msg02334.html 
> 
> you had a comment about the structure size, which I think you mean
> the struct size should be a multiple of 64 bits.

Looks like I had got mislead by there being struct
xen_domctl_sched_sedf, but it not being part of the union. I'm
sorry for that.

Jan


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