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98fa7a3e00
linux/block
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Federico Motta 98fa7a3e00 block, bfq: fix asymmetric scenarios detection 
Since commit 2d29c9f89f ("block, bfq: improve asymmetric scenarios
detection"), a scenario is defined asymmetric when one of the
following conditions holds:
- active bfq_queues have different weights
- one or more group of entities (bfq_queue or other groups of entities)
  are active
bfq grants fairness and low latency also in such asymmetric scenarios,
by plugging the dispatching of I/O if the bfq_queue in service happens
to be temporarily idle. This plugging may lower throughput, so it is
important to do it only when strictly needed.

By mistake, in commit '2d29c9f89fcd' ("block, bfq: improve asymmetric
scenarios detection") the num_active_groups counter was firstly
incremented and subsequently decremented at any entity (group or
bfq_queue) weight change.

This is useless, because only transitions from active to inactive and
vice versa matter for that counter. Unfortunately this is also
incorrect in the following case: the entity at issue is a bfq_queue
and it is under weight raising. In fact in this case there is a
spurious increment of the num_active_groups counter.

This spurious increment may cause scenarios to be wrongly detected as
asymmetric, thus causing useless plugging and loss of throughput.

This commit fixes this issue by simply removing the above useless and
wrong increments and decrements.

Fixes: 2d29c9f89f ("block, bfq: improve asymmetric scenarios detection")
Tested-by: Oleksandr Natalenko <oleksandr@natalenko.name>
Signed-off-by: Federico Motta <federico@willer.it>
Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2018-10-25 11:17:40 -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 2018-09-21 20:29:02 -06:00
bfq-iosched.c block, bfq: improve asymmetric scenarios detection 2018-10-13 15:40:00 -06:00
bfq-iosched.h block, bfq: improve asymmetric scenarios detection 2018-10-13 15:40:00 -06:00
bfq-wf2q.c block, bfq: fix asymmetric scenarios detection 2018-10-25 11:17:40 -06:00
bio-integrity.c block: remove bio_rewind_iter() 2018-09-06 15:12:24 -06:00
bio.c blkcg: reassociate bios when make_request() is called recursively 2018-10-20 15:39:55 -06:00
blk-cgroup.c This is the 4.19-rc6 release 2018-10-01 08:58:57 -06:00
blk-core.c block: add a report_zones method 2018-10-25 11:17:40 -06:00
blk-exec.c blk-mq-sched: remove unused 'can_block' arg from blk_mq_sched_insert_request 2018-01-17 09:49:21 -07:00
blk-flush.c blk-mq: change gfp flags to GFP_NOIO in blk_mq_realloc_hw_ctxs 2018-10-13 15:42:01 -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, mm: remove unnecessary __GFP_HIGH flag 2018-07-09 09:07:54 -06:00
blk-iolatency.c blk-iolatency: keep track of previous windows stats 2018-09-28 11:47:32 -06:00
blk-lib.c block: Improve zone reset execution 2018-10-25 11:17:40 -06:00
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: merge BIOVEC_SEG_BOUNDARY into biovec_phys_mergeable 2018-09-24 12:33:57 -06:00
blk-mq-cpumap.c blk-mq: don't keep offline CPUs mapped to hctx 0 2018-04-10 08:38:46 -06:00
blk-mq-debugfs-zoned.c block: Make struct request_queue smaller for CONFIG_BLK_DEV_ZONED=n 2018-07-09 09:07:52 -06:00
blk-mq-debugfs.c block: add a report_zones method 2018-10-25 11:17:40 -06:00
blk-mq-debugfs.h block: Make struct request_queue smaller for CONFIG_BLK_DEV_ZONED=n 2018-07-09 09:07:52 -06:00
blk-mq-pci.c blk-mq: code clean-up by adding an API to clear set->mq_map 2018-07-09 09:07:53 -06:00
blk-mq-rdma.c block: Add rdma affinity based queue mapping helper 2017-08-08 14:58:03 -04:00
blk-mq-sched.c blk-mq: init hctx sched after update ctx and hctx mapping 2018-08-21 09:02:55 -06:00
blk-mq-sched.h block: move call of scheduler's ->completed_request() hook 2018-09-27 17:34:52 -06:00
blk-mq-sysfs.c block drivers/block: Use octal not symbolic permissions 2018-05-24 13:38:59 -06:00
blk-mq-tag.c This is the 4.19-rc6 release 2018-10-01 08:58:57 -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 blk-mq: provide a default queue mapping for virtio device 2017-02-27 20:54:05 +02:00
blk-mq.c blk-mq: place trace_block_getrq() in correct place 2018-10-25 11:17:40 -06:00
blk-mq.h blk-mq: issue directly if hw queue isn't busy in case of 'none' 2018-07-17 16:04:00 -06:00
blk-pm.c blk-mq: Enable support for runtime power management 2018-09-26 15:11:29 -06:00
blk-pm.h block: Split blk_pm_add_request() and blk_pm_put_request() 2018-09-26 15:11:28 -06:00
blk-rq-qos.c blk-rq-qos: make depth comparisons unsigned 2018-07-22 11:30:53 -06:00
blk-rq-qos.h blk-rq-qos: make depth comparisons unsigned 2018-07-22 11:30:53 -06:00
blk-settings.c block: allow max_discard_segments to be stacked 2018-07-24 14:46:39 -06:00
blk-softirq.c blk-mq: complete req in softirq context in case of single queue 2018-10-08 10:50:43 -06:00
blk-stat.c block: export blk_stat_enable_accounting() 2018-09-27 17:34:54 -06:00
blk-stat.h blk-stat: export helpers for modifying blk_rq_stat 2018-07-09 09:07:54 -06:00
blk-sysfs.c block: Introduce blk_revalidate_disk_zones() 2018-10-25 11:17:40 -06:00
blk-tag.c for-linus-20180616 2018-06-17 05:37:55 +09:00
blk-throttle.c blkcg: consolidate bio_issue_init to be a part of core 2018-09-21 20:29:08 -06:00
blk-timeout.c blk-mq: Fix timeout handling in case the timeout handler returns BLK_EH_DONE 2018-06-23 10:25:45 -06:00
blk-wbt.c blk-wbt: wake up all when we scale up, not down 2018-10-11 13:31:28 -06:00
blk-wbt.h block: remove external dependency on wbt_flags 2018-07-09 09:07:54 -06:00
blk-zoned.c block: Introduce blk_revalidate_disk_zones() 2018-10-25 11:17:40 -06:00
blk.h block: Introduce blk_revalidate_disk_zones() 2018-10-25 11:17:40 -06:00
bounce.c block: setup bounce bio_sets properly 2018-10-21 12:05:43 -06:00
bsg-lib.c block/bsg-lib: use PTR_ERR_OR_ZERO to simplify the flow path 2018-08-01 09:13:03 -06:00
bsg.c block: bsg: move atomic_t ref_count variable to refcount API 2018-08-27 19:17:02 -06:00
cfq-iosched.c cfq: clear queue pointers from cfqg after unpinning them in cfq_pd_offline 2018-10-11 11:46:19 -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
deadline-iosched.c block drivers/block: Use octal not symbolic permissions 2018-05-24 13:38:59 -06:00
elevator.c This is the 4.19-rc6 release 2018-10-01 08:58:57 -06:00
genhd.c This is the 4.19-rc6 release 2018-10-01 08:58:57 -06:00
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 block: remove redundant 'default n' from Kconfig-s 2018-10-10 14:11:07 -06:00
Kconfig.iosched block: remove redundant 'default n' from Kconfig-s 2018-10-10 14:11:07 -06:00
kyber-iosched.c kyber: fix integer overflow of latency targets on 32-bit 2018-09-28 10:49:39 -06:00
Makefile block: Move power management code into a new source file 2018-09-26 15:11:28 -06:00
mq-deadline.c block drivers/block: Use octal not symbolic permissions 2018-05-24 13:38:59 -06:00
noop-iosched.c block: move existing elevator ops to union 2017-01-17 10:03:33 -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: use nanosecond resolution for iostat 2018-09-21 20:26:59 -06:00
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