linux/block
Paolo Valente fb53ac6cd0 block, bfq: do not idle for lowest-weight queues
In most cases, it is detrimental for throughput to plug I/O dispatch
when the in-service bfq_queue becomes temporarily empty (plugging is
performed to wait for the possible arrival, soon, of new I/O from the
in-service queue). There is however a case where plugging is needed
for service guarantees. If a bfq_queue, say Q, has a higher weight
than some other active bfq_queue, and is sync, i.e., contains sync
I/O, then, to guarantee that Q does receive a higher share of the
throughput than other lower-weight queues, it is necessary to plug I/O
dispatch when Q remains temporarily empty while being served.

For this reason, BFQ performs I/O plugging when some active bfq_queue
has a higher weight than some other active bfq_queue. But this is
unnecessarily overkill. In fact, if the in-service bfq_queue actually
has a weight lower than or equal to the other queues, then the queue
*must not* be guaranteed a higher share of the throughput than the
other queues. So, not plugging I/O cannot cause any harm to the
queue. And can boost throughput.

Taking advantage of this fact, this commit does not plug I/O for sync
bfq_queues with a weight lower than or equal to the weights of the
other queues. Here is an example of the resulting throughput boost
with the dbench workload, which is particularly nasty for BFQ. With
the dbench test in the Phoronix suite, BFQ reaches its lowest total
throughput with 6 clients on a filesystem with journaling, in case the
journaling daemon has a higher weight than normal processes. Before
this commit, the total throughput was ~80 MB/sec on a PLEXTOR PX-256M5,
after this commit it is ~100 MB/sec.

Tested-by: Holger Hoffstätte <holger@applied-asynchrony.com>
Tested-by: Oleksandr Natalenko <oleksandr@natalenko.name>
Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2019-04-01 08:15:39 -06:00
..
partitions partitions/aix: append null character to print data from disk 2018-07-27 09:17:41 -06:00
badblocks.c badblocks: fix wrong return value in badblocks_set if badblocks are disabled 2017-11-03 11:29:50 -07:00
bfq-cgroup.c blkcg: fix ref count issue with bio_blkcg() using task_css 2018-12-07 22:26:36 -07:00
bfq-iosched.c block, bfq: do not idle for lowest-weight queues 2019-04-01 08:15:39 -06:00
bfq-iosched.h block, bfq: do not idle for lowest-weight queues 2019-04-01 08:15:39 -06:00
bfq-wf2q.c block, bfq: do not idle for lowest-weight queues 2019-04-01 08:15:39 -06:00
bio-integrity.c block: remove the bio_integrity_advance export 2018-12-16 08:33:57 -07:00
bio.c block: add BIO_NO_PAGE_REF flag 2019-03-18 10:44:48 -06:00
blk-cgroup.c blkcg: Fix kernel-doc warnings 2019-03-20 14:39:09 -06:00
blk-core.c mm: refactor readahead defines in mm.h 2019-03-12 10:04:01 -07:00
blk-exec.c block: remove dead elevator code 2018-11-07 13:42:32 -07:00
blk-flush.c blk-mq: use blk_mq_put_driver_tag() to put tag 2019-03-24 10:26:16 -06:00
blk-integrity.c block: merge BIOVEC_SEG_BOUNDARY into biovec_phys_mergeable 2018-09-24 12:33:57 -06:00
blk-ioc.c block: remove the queue_lock indirection 2018-11-15 12:17:28 -07:00
blk-iolatency.c blk-iolatency: #include "blk.h" 2019-03-20 14:19:38 -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 Merge branch 'for-4.16/block' of git://git.kernel.dk/linux-block 2018-01-29 11:51:49 -08:00
blk-merge.c block: fix segment calculation for passthrough IO 2019-03-06 09:42:54 -07:00
blk-mq-cpumap.c blk-mq: initial support for multiple queue maps 2018-11-07 13:45:00 -07:00
blk-mq-debugfs-zoned.c block: Cleanup license notice 2019-01-17 21:21:40 -07:00
blk-mq-debugfs.c SCSI misc on 20190306 2019-03-09 16:53:47 -08:00
blk-mq-debugfs.h blk-mq-debugfs: support rq_qos 2018-12-16 19:53:47 -07:00
blk-mq-pci.c blk-mq: initial support for multiple queue maps 2018-11-07 13:45:00 -07:00
blk-mq-rdma.c blk-mq-rdma: pass in queue map to blk_mq_rdma_map_queues 2018-12-13 09:59:08 +01:00
blk-mq-sched.c blk-mq: save queue mapping result into ctx directly 2019-02-01 08:33:04 -07:00
blk-mq-sched.h block: mq-deadline: Fix write completion handling 2018-12-17 11:19:39 -07:00
blk-mq-sysfs.c blk-mq: export hctx->type in debugfs instead of sysfs 2018-12-17 05:44:45 -07:00
blk-mq-tag.c blk-mq: save queue mapping result into ctx directly 2019-02-01 08:33:04 -07:00
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 blk-mq: initial support for multiple queue maps 2018-11-07 13:45:00 -07:00
blk-mq.c blk-mq: fix sbitmap ws_active for shared tags 2019-03-25 13:05:47 -06:00
blk-mq.h blk-mq: use blk_mq_put_driver_tag() to put tag 2019-03-24 10:26:16 -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 blk-mq-debugfs: support rq_qos 2018-12-16 19:53:47 -07:00
blk-rq-qos.h block: fix blk-iolatency accounting underflow 2018-12-17 11:19:54 -07:00
blk-settings.c block: kill QUEUE_FLAG_FLUSH_NQ 2019-02-09 15:40:24 -07:00
blk-softirq.c block: remove a few unused exports 2018-11-15 12:13:25 -07:00
blk-stat.c block: remove a few unused exports 2018-11-15 12:13:25 -07:00
blk-stat.h block: deactivate blk_stat timer in wbt_disable_default() 2018-12-12 06:47:51 -07:00
blk-sysfs.c block: add BLK_MQ_POLL_CLASSIC for hybrid poll and return EINVAL for unexpected value 2019-03-20 14:02:07 -06:00
blk-throttle.c blkcg: consolidate bio_issue_init() to be a part of core 2018-12-07 22:26:37 -07:00
blk-timeout.c block: don't hold the queue_lock over blk_abort_request 2018-11-15 12:13:18 -07:00
blk-wbt.c blk-wbt: Declare local functions static 2019-01-24 11:09:21 -07:00
blk-wbt.h block: remove external dependency on wbt_flags 2018-07-09 09:07:54 -06:00
blk-zoned.c for-4.21/block-20181221 2018-12-28 13:19:59 -08:00
blk.h blk-mq: save queue mapping result into ctx directly 2019-02-01 08:33:04 -07:00
bounce.c block: bounce: make sure that bvec table is updated 2019-02-21 10:58:44 -07:00
bsg-lib.c scsi: bsg-lib: handle bidi requests without block layer help 2019-02-05 21:27:40 -05:00
bsg.c scsi: bsg-lib: handle bidi requests without block layer help 2019-02-05 21:27:40 -05:00
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: avoid setting none scheduler if it's already none 2019-02-11 08:21:40 -07:00
genhd.c block: Replace function name in string with __func__ 2019-02-28 14:09:08 -07:00
ioctl.c block: Introduce BLKGETNRZONES ioctl 2018-10-25 11:17:40 -06:00
ioprio.c block: add ioprio_check_cap function 2018-05-31 10:50:54 -04:00
Kconfig Kconfig updates for v4.21 2018-12-29 13:03:29 -08:00
Kconfig.iosched block: remove legacy IO schedulers 2018-11-07 13:42:32 -07:00
kyber-iosched.c kyber: use sbitmap add_wait_queue/list_del wait helpers 2018-12-20 12:17:21 -07:00
Makefile block: remove legacy IO schedulers 2018-11-07 13:42:32 -07:00
mq-deadline.c block: mq-deadline: Fix write completion handling 2018-12-17 11:19:39 -07:00
opal_proto.h block: sed-opal: Set MBRDone on S3 resume path if TPER is MBREnabled 2017-09-11 09:45:52 -06:00
partition-generic.c block: return just one value from part_in_flight 2018-12-10 08:30:38 -07:00
scsi_ioctl.c block: consistently use GFP_NOIO instead of __GFP_NORECLAIM 2018-05-14 08:55:18 -06:00
sed-opal.c block: sed-opal: Fix a couple off by one bugs 2018-06-20 12:04:06 -06:00
t10-pi.c block: move dif_prepare/dif_complete functions to block layer 2018-07-30 08:27:02 -06:00