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| author | Paolo Valente <paolo.valente@linaro.org> | 2018-09-14 16:23:09 +0200 |
|---|---|---|
| committer | Jens Axboe <axboe@kernel.dk> | 2018-09-14 13:06:05 -0600 |
| commit | c8765de0adfcaaf4ffb2d951e07444f00ffa9453 (patch) | |
| tree | 0cb59a947933733b98859b32b52df45fd80795cf /block | |
| parent | d0edc2473be9d70f999282e1ca7863ad6ae704dc (diff) | |
| download | blackbird-obmc-linux-c8765de0adfcaaf4ffb2d951e07444f00ffa9453.tar.gz blackbird-obmc-linux-c8765de0adfcaaf4ffb2d951e07444f00ffa9453.zip | |
blok, bfq: do not plug I/O if all queues are weight-raised
To reduce latency for interactive and soft real-time applications, bfq
privileges the bfq_queues containing the I/O of these
applications. These privileged queues, referred-to as weight-raised
queues, get a much higher share of the device throughput
w.r.t. non-privileged queues. To preserve this higher share, the I/O
of any non-weight-raised queue must be plugged whenever a sync
weight-raised queue, while being served, remains temporarily empty. To
attain this goal, bfq simply plugs any I/O (from any queue), if a sync
weight-raised queue remains empty while in service.
Unfortunately, this plugging typically lowers throughput with random
I/O, on devices with internal queueing (because it reduces the filling
level of the internal queues of the device).
This commit addresses this issue by restricting the cases where
plugging is performed: if a sync weight-raised queue remains empty
while in service, then I/O plugging is performed only if some of the
active bfq_queues are *not* weight-raised (which is actually the only
circumstance where plugging is needed to preserve the higher share of
the throughput of weight-raised queues). This restriction proved able
to boost throughput in really many use cases needing only maximum
throughput.
Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'block')
| -rw-r--r-- | block/bfq-iosched.c | 10 |
1 files changed, 8 insertions, 2 deletions
diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c index d94838bcc135..c0b1db3afb81 100644 --- a/block/bfq-iosched.c +++ b/block/bfq-iosched.c @@ -3580,7 +3580,12 @@ static bool bfq_better_to_idle(struct bfq_queue *bfqq) * whether bfqq is being weight-raised, because * bfq_symmetric_scenario() does not take into account also * weight-raised queues (see comments on - * bfq_weights_tree_add()). + * bfq_weights_tree_add()). In particular, if bfqq is being + * weight-raised, it is important to idle only if there are + * other, non-weight-raised queues that may steal throughput + * to bfqq. Actually, we should be even more precise, and + * differentiate between interactive weight raising and + * soft real-time weight raising. * * As a side note, it is worth considering that the above * device-idling countermeasures may however fail in the @@ -3592,7 +3597,8 @@ static bool bfq_better_to_idle(struct bfq_queue *bfqq) * to let requests be served in the desired order until all * the requests already queued in the device have been served. */ - asymmetric_scenario = bfqq->wr_coeff > 1 || + asymmetric_scenario = (bfqq->wr_coeff > 1 && + bfqd->wr_busy_queues < bfqd->busy_queues) || !bfq_symmetric_scenario(bfqd); /* |
