Re: [Xen-devel] [PATCH v1 4/4] xl: enabling XL to set per-VCPU parameters of a domain for RTDS scheduler

[Meng Xu <xumengpanda@xxxxxxxxx>]

Hi Dario,

2015-05-14 10:39 GMT-04:00 Dario Faggioli <dario.faggioli@xxxxxxxxxx>:
> On Thu, 2015-05-14 at 10:24 -0400, Meng Xu wrote:
>> > @@ -5744,6 +5749,7 @@ static int sched_rtds_pool_output(uint32_t poolid)
>> >      return 0;
>> >  }
>> >
>> > +
>> >  static int sched_default_pool_output(uint32_t poolid)
>> >  {
>> >      char *poolname;
>> > @@ -6120,38 +6126,87 @@ int main_sched_rtds(int argc, char **argv)
>> >  {
>> >      const char *dom = NULL;
>> >      const char *cpupool = NULL;
>> > -    int period = 0; /* period is in microsecond */
>> > -    int budget = 0; /* budget is in microsecond */
>> > +
>> > +    int vcpus[LIBXL_XEN_LEGACY_MAX_VCPUS]; /* indices of VCPUs that 
>> > change */
>> > +    int periods[LIBXL_XEN_LEGACY_MAX_VCPUS]; /* period is in microsecond 
>> > */
>> > +    int budgets[LIBXL_XEN_LEGACY_MAX_VCPUS]; /* budget is in microsecond 
>> > */
>>
>>
>> We know this is not good (ugly), but not sure about the best approach
>> to do this. Basically, if users tries to input several pairs of period
>> and budget, what is the best way to hold those data? Should we just
>> increase the array size by using something like remalloc when we find
>> more parameters are inputted?
>>
> In xl and/or libxl, a couple of remalloc() are not a problem. there are
> very few hot paths in them, and this is certainly not one of them.
>
> In xl, we have xrealloc() defined for that purpose, in libxl,
> GCNEW_ARRAY() and GCREALLOC_ARRAY(), so really, no big deal. It may
> might sense to put think at something to avoid realloc()-ing 17 times by
> 1 element (like doubling the allocation at each time, and then, of
> course, only use the actually filled elements).

I see. OK. This makes sense.

>
> In any case, the problem here is not (only) the static array, it is the
> use of LIBXL_XEN_LEGACY_MAX_VCPUS.

Right as you already pointed out in the libxl. :-)

Thanks,

Meng

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

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