diff options
author | Paolo Valente <paolo.valente@linaro.org> | 2019-01-29 14:06:25 +0300 |
---|---|---|
committer | Jens Axboe <axboe@kernel.dk> | 2019-01-31 22:50:22 +0300 |
commit | 20cd32450bcbec37c6d881b84bdddd8ba047ab01 (patch) | |
tree | 24b89fc7bbb5c7b302c8a75d939e92400a3998b3 /block/bfq-iosched.c | |
parent | 22cb4e681523b35f1a0eba40c25ddc1b16898801 (diff) | |
download | linux-20cd32450bcbec37c6d881b84bdddd8ba047ab01.tar.xz |
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>
Diffstat (limited to 'block/bfq-iosched.c')
-rw-r--r-- | block/bfq-iosched.c | 39 |
1 files changed, 29 insertions, 10 deletions
diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c index cd307767a134..c7a4a15c7c19 100644 --- a/block/bfq-iosched.c +++ b/block/bfq-iosched.c @@ -3274,16 +3274,32 @@ void bfq_bfqq_expire(struct bfq_data *bfqd, * requests, then the request pattern is isochronous * (see the comments on the function * bfq_bfqq_softrt_next_start()). Thus we can compute - * soft_rt_next_start. If, instead, the queue still - * has outstanding requests, then we have to wait for - * the completion of all the outstanding requests to - * discover whether the request pattern is actually - * isochronous. + * soft_rt_next_start. And we do it, unless bfqq is in + * interactive weight raising. We do not do it in the + * latter subcase, for the following reason. bfqq may + * be conveying the I/O needed to load a soft + * real-time application. Such an application will + * actually exhibit a soft real-time I/O pattern after + * it finally starts doing its job. But, if + * soft_rt_next_start is computed here for an + * interactive bfqq, and bfqq had received a lot of + * service before remaining with no outstanding + * request (likely to happen on a fast device), then + * soft_rt_next_start would be assigned such a high + * value that, for a very long time, bfqq would be + * prevented from being possibly considered as soft + * real time. + * + * If, instead, the queue still has outstanding + * requests, then we have to wait for the completion + * of all the outstanding requests to discover whether + * the request pattern is actually isochronous. */ - if (bfqq->dispatched == 0) + if (bfqq->dispatched == 0 && + bfqq->wr_coeff != bfqd->bfq_wr_coeff) bfqq->soft_rt_next_start = bfq_bfqq_softrt_next_start(bfqd, bfqq); - else { + else if (bfqq->dispatched > 0) { /* * Schedule an update of soft_rt_next_start to when * the task may be discovered to be isochronous. @@ -4834,11 +4850,14 @@ static void bfq_completed_request(struct bfq_queue *bfqq, struct bfq_data *bfqd) * isochronous, and both requisites for this condition to hold * are now satisfied, then compute soft_rt_next_start (see the * comments on the function bfq_bfqq_softrt_next_start()). We - * schedule this delayed check when bfqq expires, if it still - * has in-flight requests. + * do not compute soft_rt_next_start if bfqq is in interactive + * weight raising (see the comments in bfq_bfqq_expire() for + * an explanation). We schedule this delayed update when bfqq + * expires, if it still has in-flight requests. */ if (bfq_bfqq_softrt_update(bfqq) && bfqq->dispatched == 0 && - RB_EMPTY_ROOT(&bfqq->sort_list)) + RB_EMPTY_ROOT(&bfqq->sort_list) && + bfqq->wr_coeff != bfqd->bfq_wr_coeff) bfqq->soft_rt_next_start = bfq_bfqq_softrt_next_start(bfqd, bfqq); |