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

[George Dunlap <george.dunlap@xxxxxxxxxx>]

On 26/01/17 01:00, Dario Faggioli wrote:
> On Wed, 2017-01-18 at 03:30 -0700, Jan Beulich wrote:
>>>>> 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.
>>
> George, ping?

Yes, this looks fine then.  But it didn't apply cleanly when I tried to
apply it -- please re-send it with the other patches you have outstanding.

Thanks.
 -George


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