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Paolo Valente 13a857a4c4 block, bfq: detect wakers and unconditionally inject their I/O 
A bfq_queue Q may happen to be synchronized with another
bfq_queue Q2, i.e., the I/O of Q2 may need to be completed for Q to
receive new I/O. We call Q2 "waker queue".

If I/O plugging is being performed for Q, and Q is not receiving any
more I/O because of the above synchronization, then, thanks to BFQ's
injection mechanism, the waker queue is likely to get served before
the I/O-plugging timeout fires.

Unfortunately, this fact may not be sufficient to guarantee a high
throughput during the I/O plugging, because the inject limit for Q may
be too low to guarantee a lot of injected I/O. In addition, the
duration of the plugging, i.e., the time before Q finally receives new
I/O, may not be minimized, because the waker queue may happen to be
served only after other queues.

To address these issues, this commit introduces the explicit detection
of the waker queue, and the unconditional injection of a pending I/O
request of the waker queue on each invocation of
bfq_dispatch_request().

One may be concerned that this systematic injection of I/O from the
waker queue delays the service of Q's I/O. Fortunately, it doesn't. On
the contrary, next Q's I/O is brought forward dramatically, for it is
not blocked for milliseconds.

Reported-by: Srivatsa S. Bhat (VMware) <srivatsa@csail.mit.edu>
Tested-by: Srivatsa S. Bhat (VMware) <srivatsa@csail.mit.edu>
Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2019-06-25 09:07:34 -06:00
..
partitions block/partitions/ldm: Convert a kernel-doc header into a non-kernel-doc header 2019-05-31 15:12:34 -06:00
badblocks.c block: switch all files cleared marked as GPLv2 to SPDX tags 2019-04-30 16:11:57 -06:00
bfq-cgroup.c block: rename CONFIG_DEBUG_BLK_CGROUP to CONFIG_BFQ_CGROUP_DEBUG 2019-06-20 10:32:35 -06:00
bfq-iosched.c block, bfq: detect wakers and unconditionally inject their I/O 2019-06-25 09:07:34 -06:00
bfq-iosched.h block, bfq: detect wakers and unconditionally inject their I/O 2019-06-25 09:07:34 -06:00
bfq-wf2q.c block: switch all files cleared marked as GPLv2 or later to SPDX tags 2019-04-30 16:11:59 -06:00
bio-integrity.c block/bio-integrity: use struct_size() in kmalloc() 2019-05-16 08:48:48 -06:00
bio.c block: remove the bi_phys_segments field in struct bio 2019-06-20 10:29:22 -06:00
blk-cgroup.c blk-cgroup: move struct blkg_stat to bfq 2019-06-20 10:32:34 -06:00
blk-core.c block: update print_req_error() 2019-06-20 13:03:51 -06:00
blk-exec.c block: add SPDX tags to block layer files missing licensing information 2019-04-30 16:12:03 -06:00
blk-flush.c block: switch all files cleared marked as GPLv2 to SPDX tags 2019-04-30 16:11:57 -06:00
blk-integrity.c for-5.2/block-20190507 2019-05-07 18:14:36 -07:00
blk-ioc.c block: remove the queue_lock indirection 2018-11-15 12:17:28 -07:00
blk-iolatency.c blk-iolatency: only account submitted bios 2019-06-20 03:29:56 -06:00
blk-lib.c block: fix 32 bit overflow in __blkdev_issue_discard() 2018-11-14 08:17:18 -07:00
blk-map.c block: remove the bi_phys_segments field in struct bio 2019-06-20 10:29:22 -06:00
blk-merge.c block: untangle the end of blk_bio_segment_split 2019-06-20 10:29:22 -06:00
blk-mq-cpumap.c blk-mq: Document the blk_mq_hw_queue_to_node() arguments 2019-05-31 15:12:34 -06:00
blk-mq-debugfs-zoned.c block: Cleanup license notice 2019-01-17 21:21:40 -07:00
blk-mq-debugfs.c block: use blk_op_str() in blk-mq-debugfs.c 2019-06-20 13:03:51 -06:00
blk-mq-debugfs.h blk-mq: no need to check return value of debugfs_create functions 2019-06-13 03:00:30 -06:00
blk-mq-pci.c block: Fix blk_mq_*_map_queues() kernel-doc headers 2019-05-31 15:12:34 -06:00
blk-mq-rdma.c block: Fix blk_mq_*_map_queues() kernel-doc headers 2019-05-31 15:12:34 -06:00
blk-mq-sched.c block: remove the bi_phys_segments field in struct bio 2019-06-20 10:29:22 -06:00
blk-mq-sched.h block: remove the bi_phys_segments field in struct bio 2019-06-20 10:29:22 -06:00
blk-mq-sysfs.c for-5.2/block-20190507 2019-05-07 18:14:36 -07:00
blk-mq-tag.c block: add SPDX tags to block layer files missing licensing information 2019-04-30 16:12:03 -06:00
blk-mq-tag.h Merge branch 'for-4.15/block' of git://git.kernel.dk/linux-block 2017-11-14 15:32:19 -08:00
blk-mq-virtio.c block: Fix blk_mq_*_map_queues() kernel-doc headers 2019-05-31 15:12:34 -06:00
blk-mq.c block: remove the bi_phys_segments field in struct bio 2019-06-20 10:29:22 -06:00
blk-mq.h blk-mq: free hw queue's resource in hctx's release handler 2019-05-04 07:24:05 -06:00
blk-pm.c block: remove the queue_lock indirection 2018-11-15 12:17:28 -07:00
blk-pm.h block: remove the queue_lock indirection 2018-11-15 12:17:28 -07:00
blk-rq-qos.c block: Fix rq_qos_wait() kernel-doc header 2019-05-31 15:12:34 -06:00
blk-rq-qos.h block: add SPDX tags to block layer files missing licensing information 2019-04-30 16:12:03 -06:00
blk-settings.c block: force an unlimited segment size on queues with a virt boundary 2019-05-23 10:25:26 -06:00
blk-softirq.c block: remove a few unused exports 2018-11-15 12:13:25 -07:00
blk-stat.c block: add SPDX tags to block layer files missing licensing information 2019-04-30 16:12:03 -06:00
blk-stat.h block: deactivate blk_stat timer in wbt_disable_default() 2018-12-12 06:47:51 -07:00
blk-sysfs.c block: free sched's request pool in blk_cleanup_queue 2019-06-06 22:39:39 -06:00
blk-throttle.c block: Fix throtl_pending_timer_fn() kernel-doc header 2019-05-31 15:12:34 -06:00
blk-timeout.c block: add SPDX tags to block layer files missing licensing information 2019-04-30 16:12:03 -06:00
blk-wbt.c block: add SPDX tags to block layer files missing licensing information 2019-04-30 16:12:03 -06:00
blk-wbt.h block: remove external dependency on wbt_flags 2018-07-09 09:07:54 -06:00
blk-zoned.c block: add SPDX tags to block layer files missing licensing information 2019-04-30 16:12:03 -06:00
blk.h block: mark blk_rq_bio_prep as inline 2019-06-20 10:29:22 -06:00
bounce.c block: remove the i argument to bio_for_each_segment_all 2019-04-30 09:26:13 -06:00
bsg-lib.c block: Fix bsg_setup_queue() kernel-doc header 2019-05-31 15:12:34 -06:00
bsg.c block: switch all files cleared marked as GPLv2 to SPDX tags 2019-04-30 16:11:57 -06:00
cmdline-parser.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
compat_ioctl.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
elevator.c block: free sched's request pool in blk_cleanup_queue 2019-06-06 22:39:39 -06:00
genhd.c block: genhd: Use struct_size() helper 2019-06-15 01:46:09 -06:00
ioctl.c block: add SPDX tags to block layer files missing licensing information 2019-04-30 16:12:03 -06:00
ioprio.c block: add SPDX tags to block layer files missing licensing information 2019-04-30 16:12:03 -06:00
Kconfig block: force select mq-deadline for zoned block devices 2019-06-13 03:00:31 -06:00
Kconfig.iosched block: rename CONFIG_DEBUG_BLK_CGROUP to CONFIG_BFQ_CGROUP_DEBUG 2019-06-20 10:32:35 -06:00
kyber-iosched.c block: remove the bi_phys_segments field in struct bio 2019-06-20 10:29:22 -06:00
Makefile block: remove legacy IO schedulers 2018-11-07 13:42:32 -07:00
mq-deadline.c block: remove the bi_phys_segments field in struct bio 2019-06-20 10:29:22 -06:00
opal_proto.h block: switch all files cleared marked as GPLv2 to SPDX tags 2019-04-30 16:11:57 -06:00
partition-generic.c block: fix use-after-free on gendisk 2019-04-22 09:48:12 -06:00
scsi_ioctl.c block: switch all files cleared marked as GPLv2 to SPDX tags 2019-04-30 16:11:57 -06:00
sed-opal.c block: switch all files cleared marked as GPLv2 to SPDX tags 2019-04-30 16:11:57 -06:00
t10-pi.c block: switch all files cleared marked as GPLv2 to SPDX tags 2019-04-30 16:11:57 -06:00