block, bfq: reduce latency during request-pool saturation
authorPaolo Valente <paolo.valente@linaro.org>
Wed, 12 Apr 2017 16:23:15 +0000 (18:23 +0200)
committerJens Axboe <axboe@fb.com>
Wed, 19 Apr 2017 14:30:26 +0000 (08:30 -0600)
commitcfd69712a101f528caad1529e64834e31e5dff62
treecfe6110f6cec2a2735035b0a7f0aea533a12f1e2
parentbcd5642607ab9195e22a1617d92fb82698d44448
block, bfq: reduce latency during request-pool saturation

This patch introduces an heuristic that reduces latency when the
I/O-request pool is saturated. This goal is achieved by disabling
device idling, for non-weight-raised queues, when there are weight-
raised queues with pending or in-flight requests. In fact, as
explained in more detail in the comment on the function
bfq_bfqq_may_idle(), this reduces the rate at which processes
associated with non-weight-raised queues grab requests from the pool,
thereby increasing the probability that processes associated with
weight-raised queues get a request immediately (or at least soon) when
they need one. Along the same line, if there are weight-raised queues,
then this patch halves the service rate of async (write) requests for
non-weight-raised queues.

Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Signed-off-by: Arianna Avanzini <avanzini.arianna@gmail.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
block/bfq-iosched.c