Re: [Xen-devel] [PATCH] xen: credit2: clear bit instead of skip step in runq_tickle()

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 18.01.17 at 11:21, <george.dunlap@xxxxxxxxxx> wrote:
> On 18/01/17 00:30, Dario Faggioli wrote:
>> index ef8e0d8..d086264 100644
>> --- a/xen/common/sched_credit2.c
>> +++ b/xen/common/sched_credit2.c
>> @@ -985,7 +985,7 @@ runq_tickle(const struct scheduler *ops, struct 
>> csched2_vcpu *new, s_time_t now)
>>      cpumask_andnot(&mask, &rqd->active, &rqd->idle);
>>      cpumask_andnot(&mask, &mask, &rqd->tickled);
>>      cpumask_and(&mask, &mask, new->vcpu->cpu_hard_affinity);
>> -    if ( cpumask_test_cpu(cpu, &mask) )
>> +    if ( __cpumask_test_and_clear_cpu(cpu, &mask) )
> 
> Since we're micro-optimizing -- isn't test-and-clear a locked operation?
>  Would that be more expensive than the if() statement below?

cpumask_test_and_clear_cpu() is, but __cpumask_test_and_clear_cpu()
isn't.

Jan


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