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Luca Miccio
a33801e8b4
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 <[email protected]> Suggested-by: Ulf Hansson <[email protected]> Tested-by: Lee Tibbert <[email protected]> Tested-by: Oleksandr Natalenko <[email protected]> Signed-off-by: Luca Miccio <[email protected]> Signed-off-by: Paolo Valente <[email protected]> Signed-off-by: Jens Axboe <[email protected]>