From 38c9140740eb0993924b676a111c164903163b1e Mon Sep 17 00:00:00 2001 From: Hou Tao Date: Wed, 12 Jul 2017 15:25:01 +0800 Subject: bfq: fix typos in comments about B-WF2Q+ algorithm The start time of eligible entity should be less than or equal to the current virtual time, and the entity in idle tree has a finish time being greater than the current virtual time. Signed-off-by: Hou Tao Reviewed-by: Paolo Valente Signed-off-by: Jens Axboe --- block/bfq-iosched.h | 2 +- block/bfq-wf2q.c | 2 +- 2 files changed, 2 insertions(+), 2 deletions(-) (limited to 'block') diff --git a/block/bfq-iosched.h b/block/bfq-iosched.h index 8fd83b885774..63e771ab56d8 100644 --- a/block/bfq-iosched.h +++ b/block/bfq-iosched.h @@ -52,7 +52,7 @@ struct bfq_entity; struct bfq_service_tree { /* tree for active entities (i.e., those backlogged) */ struct rb_root active; - /* tree for idle entities (i.e., not backlogged, with V <= F_i)*/ + /* tree for idle entities (i.e., not backlogged, with V < F_i)*/ struct rb_root idle; /* idle entity with minimum F_i */ diff --git a/block/bfq-wf2q.c b/block/bfq-wf2q.c index 5ec05cd42b80..979f8f21b7e2 100644 --- a/block/bfq-wf2q.c +++ b/block/bfq-wf2q.c @@ -1297,7 +1297,7 @@ static void bfq_update_vtime(struct bfq_service_tree *st, u64 new_value) * * This function searches the first schedulable entity, starting from the * root of the tree and going on the left every time on this side there is - * a subtree with at least one eligible (start >= vtime) entity. The path on + * a subtree with at least one eligible (start <= vtime) entity. The path on * the right is followed only if a) the left subtree contains no eligible * entities and b) no eligible entity has been found yet. */ -- cgit v1.2.3 From 3f7cb4f4130ca5693f0698211bf1e42945efbb8c Mon Sep 17 00:00:00 2001 From: Hou Tao Date: Tue, 11 Jul 2017 21:58:15 +0800 Subject: bfq: dispatch request to prevent queue stalling after the request completion There are mq devices (eg., virtio-blk, nbd and loopback) which don't invoke blk_mq_run_hw_queues() after the completion of a request. If bfq is enabled on these devices and the slice_idle attribute or strict_guarantees attribute is set as zero, it is possible that after a request completion the remaining requests of busy bfq queue will stalled in the bfq schedule until a new request arrives. To fix the scheduler latency problem, we need to check whether or not all issued requests have completed and dispatch more requests to driver if there is no request in driver. The problem can be reproduced by running the following script on a virtio-blk device with nr_hw_queues as 1: #!/bin/sh dev=vdb # mount point for dev mp=/tmp/mnt cd $mp job=strict.job cat < $job [global] direct=1 bs=4k size=256M rw=write ioengine=libaio iodepth=128 runtime=5 time_based [1] filename=1.data [2] new_group filename=2.data EOF echo bfq > /sys/block/$dev/queue/scheduler echo 1 > /sys/block/$dev/queue/iosched/strict_guarantees fio $job Signed-off-by: Hou Tao Reviewed-by: Paolo Valente Signed-off-by: Jens Axboe --- block/bfq-iosched.c | 3 +++ 1 file changed, 3 insertions(+) (limited to 'block') diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c index 60a6835265fc..436b6ca6b175 100644 --- a/block/bfq-iosched.c +++ b/block/bfq-iosched.c @@ -4299,6 +4299,9 @@ static void bfq_completed_request(struct bfq_queue *bfqq, struct bfq_data *bfqd) bfq_bfqq_expire(bfqd, bfqq, false, BFQQE_NO_MORE_REQUESTS); } + + if (!bfqd->rq_in_driver) + bfq_schedule_dispatch(bfqd); } static void bfq_put_rq_priv_body(struct bfq_queue *bfqq) -- cgit v1.2.3