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

[Chong Li <lichong659@xxxxxxxxx>]

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.

Chong


-- 
Chong Li
Department of Computer Science and Engineering
Washington University in St.louis

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