Re: [Xen-devel] [PATCH v3 for Xen 4.6 3/4] libxl: enable per-VCPU parameter settings for RTDS scheduler

[Meng Xu <xumengpanda@xxxxxxxxx>]

Hi Ian,

2015-06-30 9:19 GMT-07:00 Ian Campbell <ian.campbell@xxxxxxxxxx>:
> On Tue, 2015-06-30 at 11:10 -0500, Chong Li wrote:
>> On Tue, Jun 30, 2015 at 10:57 AM, Ian Campbell <ian.campbell@xxxxxxxxxx> 
>> wrote:
>> > On Tue, 2015-06-30 at 10:42 -0500, Chong Li wrote:
>> >> >> @@ -1554,10 +1564,17 @@ int libxl_sched_credit_params_set(libxl_ctx 
>> >> >> *ctx, uint32_t poolid,
>> >> >>  #define LIBXL_DOMAIN_SCHED_PARAM_EXTRATIME_DEFAULT -1
>> >> >>  #define LIBXL_DOMAIN_SCHED_PARAM_BUDGET_DEFAULT    -1
>> >> >>
>> >> >> +/* Per-VCPU parameters*/
>> >> >> +#define LIBXL_DOMAIN_SCHED_PARAM_VCPU_INDEX_DEFAULT -1
>> >> >
>> >> > What is the effect of passing vcpuid == -1 to this interface?
>> >>
>> >> I think the right way should be:
>> >>
>> >> #define LIBXL_SCHED_PARAM_VCPU_INDEX_DEFAULT -1
>> >>
>> >> which is the default value for the vcpuid in libxl_sched_params. Even
>> >> though libxl_sched_params is used for per-vcpu settings, all the other
>> >> fields (except vcpuid) would still use
>> >> LIBXL_DOMAIN_SCHED_PARAM_*_DEFAULT values, just for convenience.
>> >
>> > My question is what does the concept of vcpu==-1 mean in this interface?
>>
>> We need a default value for vcpuid when initiating libxl_sched_params,
>> just like other fields (e.g., budget, weight ...) in the struct. But
>> the default value could be others, maybe "0". I'm not sure.
>
> What will you do if you come across a -1 in this field? What are the
> semantics of the interface WRT this field.
>
> Note that this field is not the same as the others in this struct, it is
> in effect part of the "key" while the others are the "values".
>

vcpuid in the libxl is not the key but the value.

When it is passed into hypervisor, vcpuid acts as the key to identify
which VCPU. vcpuid should be be negative when it is passed to
hypervisor.

Do you have any concerns about assigning the initial value of vcpuid as -1?

Thanks,

Meng


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

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