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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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