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block, bfq: do not consider interactive queues in srt filtering
The speed at which a bfq_queue receives I/O is one of the parameters by which bfq decides whether the queue is soft real-time (i.e., whether the queue contains the I/O of a soft real-time application). In particular, when a bfq_queue remains without outstanding I/O requests, bfq computes the minimum time instant, named soft_rt_next_start, at which the next request of the queue may arrive for the queue to be deemed as soft real time. Unfortunately this filtering may cause problems with a queue in interactive weight raising. In fact, such a queue may be conveying the I/O needed to load a soft real-time application. The latter will actually exhibit a soft real-time I/O pattern after it finally starts doing its job. But, if soft_rt_next_start is updated for an interactive bfq_queue, and the queue has received a lot of service before remaining with no outstanding request (likely to happen on a fast device), then soft_rt_next_start is assigned such a high value that, for a very long time, the queue is prevented from being possibly considered as soft real time. This commit removes the updating of soft_rt_next_start for bfq_queues in interactive weight raising. Signed-off-by: Paolo Valente <paolo.valente@linaro.org> Signed-off-by: Jens Axboe <axboe@kernel.dk>
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@ -3274,16 +3274,32 @@ void bfq_bfqq_expire(struct bfq_data *bfqd,
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* requests, then the request pattern is isochronous
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* (see the comments on the function
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* bfq_bfqq_softrt_next_start()). Thus we can compute
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* soft_rt_next_start. If, instead, the queue still
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* has outstanding requests, then we have to wait for
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* the completion of all the outstanding requests to
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* discover whether the request pattern is actually
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* isochronous.
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* soft_rt_next_start. And we do it, unless bfqq is in
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* interactive weight raising. We do not do it in the
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* latter subcase, for the following reason. bfqq may
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* be conveying the I/O needed to load a soft
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* real-time application. Such an application will
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* actually exhibit a soft real-time I/O pattern after
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* it finally starts doing its job. But, if
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* soft_rt_next_start is computed here for an
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* interactive bfqq, and bfqq had received a lot of
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* service before remaining with no outstanding
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* request (likely to happen on a fast device), then
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* soft_rt_next_start would be assigned such a high
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* value that, for a very long time, bfqq would be
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* prevented from being possibly considered as soft
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* real time.
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*
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* If, instead, the queue still has outstanding
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* requests, then we have to wait for the completion
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* of all the outstanding requests to discover whether
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* the request pattern is actually isochronous.
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*/
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if (bfqq->dispatched == 0)
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if (bfqq->dispatched == 0 &&
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bfqq->wr_coeff != bfqd->bfq_wr_coeff)
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bfqq->soft_rt_next_start =
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bfq_bfqq_softrt_next_start(bfqd, bfqq);
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else {
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else if (bfqq->dispatched > 0) {
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/*
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* Schedule an update of soft_rt_next_start to when
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* the task may be discovered to be isochronous.
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@ -4834,11 +4850,14 @@ static void bfq_completed_request(struct bfq_queue *bfqq, struct bfq_data *bfqd)
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* isochronous, and both requisites for this condition to hold
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* are now satisfied, then compute soft_rt_next_start (see the
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* comments on the function bfq_bfqq_softrt_next_start()). We
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* schedule this delayed check when bfqq expires, if it still
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* has in-flight requests.
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* do not compute soft_rt_next_start if bfqq is in interactive
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* weight raising (see the comments in bfq_bfqq_expire() for
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* an explanation). We schedule this delayed update when bfqq
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* expires, if it still has in-flight requests.
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*/
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if (bfq_bfqq_softrt_update(bfqq) && bfqq->dispatched == 0 &&
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RB_EMPTY_ROOT(&bfqq->sort_list))
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RB_EMPTY_ROOT(&bfqq->sort_list) &&
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bfqq->wr_coeff != bfqd->bfq_wr_coeff)
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bfqq->soft_rt_next_start =
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bfq_bfqq_softrt_next_start(bfqd, bfqq);
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