Re: [Xen-devel] [PATCH v4] xen: sched_rt: print useful affinity info when dumping

[Meng Xu <xumengpanda@xxxxxxxxx>]

>
>> 2015-05-12 10:06 GMT-04:00 Dario Faggioli <dario.faggioli@xxxxxxxxxx>:
>
>> > --- a/xen/common/sched_rt.c
>> > +++ b/xen/common/sched_rt.c
>> > @@ -124,6 +124,24 @@
>> >  #define TRC_RTDS_BUDGET_REPLENISH TRC_SCHED_CLASS_EVT(RTDS, 4)
>> >  #define TRC_RTDS_SCHED_TASKLET    TRC_SCHED_CLASS_EVT(RTDS, 5)
>> >
>> > + /*
>> > +  * Useful to avoid too many cpumask_var_t on the stack.
>> > +  */
>> > +static cpumask_t **_cpumask_scratch;
>> > +#define cpumask_scratch _cpumask_scratch[smp_processor_id()]
>>
>> The cpumask_scratch seems never used in this patch.. Did I miss anything?
>>
> No, it's never used, because, as it happens, the use case this patch
> deals with needs to explicitly reference the _cpumask_scratch array.
> That should be the exception rather than the rule, and the reason why it
> is necessary this time is given in the comments.
>
>> If it's not used in any other places, do we really need this #define?
>>
> We do, IMO. The changelog says that, in addition to improving the dump
> output, this change puts in place a "scratch cpumask machinery", useful
> to reduce the use of either on stack or dynamically allocated cpumask-s.
> That #define is part of the machinery, as it is what people should use
> everywhere (possible), to reference the scratch bitmap.

OK. I see the reason here.

>
> So, let me ask a question myself: when can we expect a patch that takes
> advantage of the scratch cpumask machinery being introduced here, in
> order to get rid of some (most, hopefully) of the cpumask_t and
> cpumask_var_t all around sched_rt.c? :-D
>
> When that will happen, you'll need that #define, and if I kill it from
> here, you'll have to introduce it yourself. As said, I like it being
> introduced here better, but can live with you adding it with your
> patch(es), if that's what everyone else prefer.

I'm ok with either way and prefer the way you do it. :-)


Reviewed-by: Meng Xu <mengxu@xxxxxxxxxxxxx>

Thanks,

Meng

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

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