@@ -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);
/*
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> --- block/bfq-iosched.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-)