linux/Documentation/block
Luca Miccio a33801e8b4 block, bfq: move debug blkio stats behind CONFIG_DEBUG_BLK_CGROUP
BFQ currently creates, and updates, its own instance of the whole
set of blkio statistics that cfq creates. Yet, from the comments
of Tejun Heo in [1], it turned out that most of these statistics
are meant/useful only for debugging. This commit makes BFQ create
the latter, debugging statistics only if the option
CONFIG_DEBUG_BLK_CGROUP is set.

By doing so, this commit also enables BFQ to enjoy a high perfomance
boost. The reason is that, if CONFIG_DEBUG_BLK_CGROUP is not set, then
BFQ has to update far fewer statistics, and, in particular, not the
heaviest to update.  To give an idea of the benefits, if
CONFIG_DEBUG_BLK_CGROUP is not set, then, on an Intel i7-4850HQ, and
with 8 threads doing random I/O in parallel on null_blk (configured
with 0 latency), the throughput of BFQ grows from 310 to 400 KIOPS
(+30%). We have measured similar or even much higher boosts with other
CPUs: e.g., +45% with an ARM CortexTM-A53 Octa-core. Our results have
been obtained and can be reproduced very easily with the script in [1].

[1] https://www.spinics.net/lists/linux-block/msg18943.html

Suggested-by: Tejun Heo <tj@kernel.org>
Suggested-by: Ulf Hansson <ulf.hansson@linaro.org>
Tested-by: Lee Tibbert <lee.tibbert@gmail.com>
Tested-by: Oleksandr Natalenko <oleksandr@natalenko.name>
Signed-off-by: Luca Miccio <lucmiccio@gmail.com>
Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2017-11-14 20:13:33 -07:00
..
00-INDEX
bfq-iosched.txt block, bfq: move debug blkio stats behind CONFIG_DEBUG_BLK_CGROUP 2017-11-14 20:13:33 -07:00
biodoc.txt block: remove __bio_kmap_atomic 2017-11-10 19:53:25 -07:00
biovecs.txt
capability.txt
cfq-iosched.txt
cmdline-partition.txt
data-integrity.txt bio-integrity: fold bio_integrity_enabled to bio_integrity_prep 2017-07-03 16:56:24 -06:00
deadline-iosched.txt
ioprio.txt
kyber-iosched.txt
null_blk.txt null_blk: add an usage for shared tags in documentation 2017-11-07 09:25:37 -07:00
pr.txt
queue-sysfs.txt
request.txt
stat.txt
switching-sched.txt
writeback_cache_control.txt