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Paolo Valente a52a69ea89 block, bfq: limit tags for writes and async I/O 
Asynchronous I/O can easily starve synchronous I/O (both sync reads
and sync writes), by consuming all request tags. Similarly, storms of
synchronous writes, such as those that sync(2) may trigger, can starve
synchronous reads. In their turn, these two problems may also cause
BFQ to loose control on latency for interactive and soft real-time
applications. For example, on a PLEXTOR PX-256M5S SSD, LibreOffice
Writer takes 0.6 seconds to start if the device is idle, but it takes
more than 45 seconds (!) if there are sequential writes in the
background.

This commit addresses this issue by limiting the maximum percentage of
tags that asynchronous I/O requests and synchronous write requests can
consume. In particular, this commit grants a higher threshold to
synchronous writes, to prevent the latter from being starved by
asynchronous I/O.

According to the above test, LibreOffice Writer now starts in about
1.2 seconds on average, regardless of the background workload, and
apart from some rare outlier. To check this improvement, run, e.g.,
sudo ./comm_startup_lat.sh bfq 5 5 seq 10 "lowriter --terminate_after_init"
for the comm_startup_lat benchmark in the S suite [1].

[1] https://github.com/Algodev-github/S

Tested-by: Oleksandr Natalenko <oleksandr@natalenko.name>
Tested-by: Holger Hoffstätte <holger@applied-asynchrony.com>
Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
 		2018-01-18 08:21:35 -07:00
..
partitions partitions/msdos: Unable to mount UFS 44bsd partitions 2018-01-10 09:12:16 -07:00
Kconfig License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
Kconfig.iosched License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
Makefile License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
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 block, bfq: put async queues for root bfq groups too 2018-01-09 08:45:25 -07:00
bfq-iosched.c block, bfq: limit tags for writes and async I/O 2018-01-18 08:21:35 -07:00
bfq-iosched.h block, bfq: limit tags for writes and async I/O 2018-01-18 08:21:35 -07:00
bfq-wf2q.c block, bfq: let a queue be merged only shortly after starting I/O 2018-01-05 09:26:09 -07:00
bio-integrity.c block: Fix __bio_integrity_endio() documentation 2018-01-17 09:59:33 -07:00
bio.c block: move bio_alloc_pages() to bcache 2018-01-06 09:18:00 -07:00
blk-cgroup.c blkcg: add sanity check for blkcg policy operations 2017-11-04 12:31:15 -06:00
blk-core.c blk-mq: improve DM's blk-mq IO merging via blk_insert_cloned_request feedback 2018-01-17 09:46:54 -07:00
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: don't allocate driver tag upfront for flush rq 2017-11-04 12:40:13 -06:00
blk-integrity.c block: switch bios to blk_status_t 2017-06-09 09:27:32 -06:00
blk-ioc.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
blk-lib.c Merge branch 'for-4.15/block' of git://git.kernel.dk/linux-block 2017-11-14 15:32:19 -08:00
blk-map.c blk_rq_map_user_iov: fix error override 2018-01-15 08:50:32 -07:00
blk-merge.c Revert "block: blk-merge: try to make front segments in full size" 2018-01-09 20:23:19 -07:00
blk-mq-cpumap.c blk-mq: map queues to all present CPUs 2017-07-24 10:01:31 -06:00
blk-mq-debugfs.c blk-mq: add missing RQF_STARTED to debugfs 2018-01-12 14:47:57 -07:00
blk-mq-debugfs.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
blk-mq-pci.c blk-mq-pci: add a fallback when pci_irq_get_affinity returns NULL 2017-08-18 08:08:14 -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-sched: remove unused 'can_block' arg from blk_mq_sched_insert_request 2018-01-17 09:49:21 -07:00
blk-mq-sched.h blk-mq-sched: remove unused 'can_block' arg from blk_mq_sched_insert_request 2018-01-17 09:49:21 -07:00
blk-mq-sysfs.c block: properly protect the 'queue' kobj in blk_unregister_queue 2018-01-15 08:41:38 -07:00
blk-mq-tag.c blk-mq: improve heavily contended tag case 2017-12-22 11:09:37 -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: provide a default queue mapping for virtio device 2017-02-27 20:54:05 +02:00
blk-mq.c blk-mq: don't dispatch request in blk_mq_request_direct_issue if queue is busy 2018-01-17 21:38:52 -07:00
blk-mq.h blk-mq: improve DM's blk-mq IO merging via blk_insert_cloned_request feedback 2018-01-17 09:46:54 -07:00
blk-settings.c block: remove __bio_kmap_atomic 2017-11-10 19:53:25 -07:00
blk-softirq.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
blk-stat.c treewide: setup_timer() -> timer_setup() 2017-11-21 15:57:07 -08:00
blk-stat.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
blk-sysfs.c block: allow gendisk's request_queue registration to be deferred 2018-01-15 08:41:38 -07:00
blk-tag.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
blk-throttle.c treewide: setup_timer() -> timer_setup() 2017-11-21 15:57:07 -08:00
blk-timeout.c block: add accessors for setting/querying request deadline 2018-01-10 11:47:47 -07:00
blk-wbt.c blk-wbt: fix comments typo 2017-11-23 22:00:20 -07:00
blk-wbt.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
blk-zoned.c block: introduce zoned block devices zone write locking 2018-01-05 09:22:17 -07:00
blk.h block: convert REQ_ATOM_COMPLETE to stealing rq->__deadline bit 2018-01-10 11:47:53 -07:00
bounce.c block: bounce: don't access bio->bi_io_vec in copy_to_high_bio_irq 2018-01-06 09:18:00 -07:00
bsg-lib.c block: Fix kernel-doc warnings reported when building with W=1 2018-01-09 11:15:17 -07:00
bsg.c block: pass full fmode_t to blk_verify_command 2017-11-10 19:53:25 -07:00
cfq-iosched.c block/cfq: cache rightmost rb_node 2017-09-08 18:26:49 -07:00
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 deadline-iosched: Introduce zone locking support 2018-01-05 09:22:17 -07:00
elevator.c blk-mq: quiesce queue during switching io sched and updating nr_requests 2018-01-06 09:25:36 -07:00
genhd.c block: allow gendisk's request_queue registration to be deferred 2018-01-15 08:41:38 -07:00
ioctl.c block: move CAP_SYS_ADMIN check in blkdev_roset() 2017-10-25 12:25:00 -06:00
ioprio.c block: Add fallthrough markers to switch statements 2017-06-21 11:46:07 -06:00
kyber-iosched.c block: kyber: check if there are requests in ctx in kyber_has_work() 2017-11-01 08:20:02 -06:00
mq-deadline.c mq-deadline: make it clear that __dd_dispatch_request() works on all hw queues 2018-01-06 09:23:11 -07:00
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 License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
scsi_ioctl.c block: silently forbid sending any ioctl to a partition 2018-01-10 12:30:37 -07:00
sed-opal.c block: sed-opal: Set MBRDone on S3 resume path if TPER is MBREnabled 2017-09-11 09:45:52 -06:00
t10-pi.c t10-pi: Move opencoded contants to common header 2017-07-03 16:56:25 -06:00