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SubjectRe: [PATCH 05/24] io-controller: Modify cfq to make use of flat elevator fair queuing
Vivek Goyal wrote:
...
> /*
> * Check if new_cfqq should preempt the currently active queue. Return 0 for
> - * no or if we aren't sure, a 1 will cause a preempt.
> + * no or if we aren't sure, a 1 will cause a preemption attempt.
> + * Some of the preemption logic has been moved to common layer. Only cfq
> + * specific parts are left here.
> */
> static int
> -cfq_should_preempt(struct cfq_data *cfqd, struct cfq_queue *new_cfqq,
> - struct request *rq)
> +cfq_should_preempt(struct request_queue *q, void *new_cfqq, struct request *rq)
> {
> - struct cfq_queue *cfqq;
> + struct cfq_data *cfqd = q->elevator->elevator_data;
> + struct cfq_queue *cfqq = elv_active_sched_queue(q->elevator);
>
> - cfqq = cfqd->active_queue;
> if (!cfqq)
> return 0;
>
> - if (cfq_slice_used(cfqq))
> + if (elv_ioq_slice_used(cfqq->ioq))
> return 1;
>
> if (cfq_class_idle(new_cfqq))
> @@ -2018,13 +1661,7 @@ cfq_should_preempt(struct cfq_data *cfqd, struct cfq_queue *new_cfqq,
> if (rq_is_meta(rq) && !cfqq->meta_pending)
> return 1;
>
> - /*
> - * Allow an RT request to pre-empt an ongoing non-RT cfqq timeslice.
> - */
> - if (cfq_class_rt(new_cfqq) && !cfq_class_rt(cfqq))
> - return 1;
> -
> - if (!cfqd->active_cic || !cfq_cfqq_wait_request(cfqq))
> + if (!cfqd->active_cic || !elv_ioq_wait_request(cfqq->ioq))
> return 0;
>
> /*

Hi Vivek,

cfq_should_preempt() will do the check "if (cfq_rq_close(cfqd, rq)) to see whether
it should preempt the current cfqq. From fairness point of view, should we also
check "fairness" value, if it's set fairness == 1, don't allow to preempt the current
cfqq?

--
Regards
Gui Jianfeng



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