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authorLuca Miccio <lucmiccio@gmail.com>2017-11-13 09:34:10 +0300
committerJens Axboe <axboe@kernel.dk>2017-11-15 06:13:33 +0300
commita33801e8b4735b8d473f963e5854172f9cde3e8b (patch)
treeacebf1dbfbe5effb178f76d31b841b9fb24f45fd /block/bfq-iosched.h
parent24bfd19bb7890255693ee5cb6dc100d8d215d00b (diff)
downloadlinux-a33801e8b4735b8d473f963e5854172f9cde3e8b.tar.xz
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>
Diffstat (limited to 'block/bfq-iosched.h')
-rw-r--r--block/bfq-iosched.h4
1 files changed, 2 insertions, 2 deletions
diff --git a/block/bfq-iosched.h b/block/bfq-iosched.h
index ac0809c72c98..91c4390903a1 100644
--- a/block/bfq-iosched.h
+++ b/block/bfq-iosched.h
@@ -689,7 +689,7 @@ enum bfqq_expiration {
};
struct bfqg_stats {
-#ifdef CONFIG_BFQ_GROUP_IOSCHED
+#if defined(CONFIG_BFQ_GROUP_IOSCHED) && defined(CONFIG_DEBUG_BLK_CGROUP)
/* number of ios merged */
struct blkg_rwstat merged;
/* total time spent on device in ns, may not be accurate w/ queueing */
@@ -717,7 +717,7 @@ struct bfqg_stats {
uint64_t start_idle_time;
uint64_t start_empty_time;
uint16_t flags;
-#endif /* CONFIG_BFQ_GROUP_IOSCHED */
+#endif /* CONFIG_BFQ_GROUP_IOSCHED && CONFIG_DEBUG_BLK_CGROUP */
};
#ifdef CONFIG_BFQ_GROUP_IOSCHED