linux-kernel - BFQ speed tests [was Re: [PATCH RFC - TAKE TWO - 00/12] New version of the BFQ I/O Scheduler]

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Date:	Wed, 4 Jun 2014 12:03:58 +0200
From:	Pavel Machek <pavel@....cz>
To:	Paolo Valente <paolo.valente@...more.it>
Cc:	Tejun Heo <tj@...nel.org>, Jens Axboe <axboe@...nel.dk>,
	Li Zefan <lizefan@...wei.com>,
	Fabio Checconi <fchecconi@...il.com>,
	Arianna Avanzini <avanzini.arianna@...il.com>,
	linux-kernel@...r.kernel.org,
	containers@...ts.linux-foundation.org, cgroups@...r.kernel.org
Subject: BFQ speed tests [was Re: [PATCH RFC - TAKE TWO - 00/12] New
 version of the BFQ I/O Scheduler]

Hi!

> Should this attempt be useless as well, I will, if you do not mind, try by asking you more details about your system and reproducing your configuration as much as I can.
> 

Try making BFQ the default scheduler. That seems to break it for me,
when selected at runtime, it looks stable.

Anyway, here are some speed tests. Background load:

root@duo:/data/tmp# echo cfq > /sys/block/sda/queue/scheduler 
root@duo:/data/tmp# echo 3 > /proc/sys/vm/drop_caches
root@duo:/data/tmp# cat /dev/zero > delme; cat /dev/zero > delme;cat
/dev/zero > delme;cat /dev/zero > delme;cat /dev/zero > delme;cat
/dev/zero > delme

(Machine was running out of disk space.)

(I alternate between cfq and bfq).

Benchmark. I chose git describe because it is part of kernel build
sometimes .. and I actually wait for that.

pavel@duo:/data/l/linux-good$ time git describe
warning: refname 'HEAD' is ambiguous.
v3.15-rc8-144-g405dedd

Unfortunately, results are not too good for BFQ. (Can you replicate
the results?)

# BFQ
10.24user 1.62system 467.02 (7m47.028s) elapsed 2.54%CPU
# CFQ
8.55user 1.26system 69.57 (1m9.577s) elapsed 14.11%CPU
# BFQ
11.70user 3.18system 1491.59 (24m51.599s) elapsed 0.99%CPU
# CFQ, no background load
8.51user 0.75system 30.99 (0m30.994s) elapsed 29.91%CPU
# CFQ
8.70user 1.36system 74.72 (1m14.720s) elapsed 13.48%CPU

									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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