Date: Wed, 5 Oct 2016 11:30:53 -0700
From: Shaohua Li <shli@fb.com>
To: Tejun Heo <tj@kernel.org>
CC: Paolo Valente <paolo.valente@unimore.it>,
        Vivek Goyal <vgoyal@redhat.com>, <linux-block@vger.kernel.org>,
        <linux-kernel@vger.kernel.org>, Jens Axboe <axboe@fb.com>,
        <Kernel-team@fb.com>, <jmoyer@redhat.com>,
        Mark Brown <broonie@kernel.org>,
        Linus Walleij <linus.walleij@linaro.org>,
        Ulf Hansson <ulf.hansson@linaro.org>
Subject: Re: [PATCH V3 00/11] block-throttle: add .high limit
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On Wed, Oct 05, 2016 at 10:49:46AM -0400, Tejun Heo wrote:
> Hello, Paolo.
> 
> On Wed, Oct 05, 2016 at 02:37:00PM +0200, Paolo Valente wrote:
> > In this respect, for your generic, unpredictable scenario to make
> > sense, there must exist at least one real system that meets the
> > requirements of such a scenario.  Or, if such a real system does not
> > yet exist, it must be possible to emulate it.  If it is impossible to
> > achieve this last goal either, then I miss the usefulness
> > of looking for solutions for such a scenario.
> > 
> > That said, let's define the instance(s) of the scenario that you find
> > most representative, and let's test BFQ on it/them.  Numbers will give
> > us the answers.  For example, what about all or part of the following
> > groups:
> > . one cyclically doing random I/O for some second and then sequential I/O
> > for the next seconds
> > . one doing, say, quasi-sequential I/O in ON/OFF cycles
> > . one starting an application cyclically
> > . one playing back or streaming a movie
> > 
> > For each group, we could then measure the time needed to complete each
> > phase of I/O in each cycle, plus the responsiveness in the group
> > starting an application, plus the frame drop in the group streaming
> > the movie.  In addition, we can measure the bandwidth/iops enjoyed by
> > each group, plus, of course, the aggregate throughput of the whole
> > system.  In particular we could compare results with throttling, BFQ,
> > and CFQ.
> > 
> > Then we could write resulting numbers on the stone, and stick to them
> > until something proves them wrong.
> > 
> > What do you (or others) think about it?
> 
> That sounds great and yeah it's lame that we didn't start with that.
> Shaohua, would it be difficult to compare how bfq performs against
> blk-throttle?

I had a test of BFQ. I'm using BFQ found at
http://algogroup.unimore.it/people/paolo/disk_sched/sources.php. version is
4.7.0-v8r3. It's a LSI SSD, queue depth 32. I use default setting. fio script
is:

[global]
ioengine=libaio
direct=1
readwrite=randread
bs=4k
runtime=60
time_based=1
file_service_type=random:36
overwrite=1
thread=0
group_reporting=1
filename=/dev/sdb
iodepth=1
numjobs=8

[groupA]
prio=2

[groupB]
new_group
prio=6

I'll change iodepth, numjobs and prio in different tests. result unit is MB/s.

iodepth=1 numjobs=1 prio 4:4
CFQ: 28:28 BFQ: 21:21 deadline: 29:29

iodepth=8 numjobs=1 prio 4:4
CFQ: 162:162 BFQ: 102:98 deadline: 205:205

iodepth=1 numjobs=8 prio 4:4
CFQ: 157:157 BFQ: 81:92 deadline: 196:197

iodepth=1 numjobs=1 prio 2:6
CFQ: 26.7:27.6 BFQ: 20:6 deadline: 29:29

iodepth=8 numjobs=1 prio 2:6
CFQ: 166:174 BFQ: 139:72  deadline: 202:202

iodepth=1 numjobs=8 prio 2:6
CFQ: 148:150 BFQ: 90:77 deadline: 198:197

CFQ isn't fair at all. BFQ is very good in this side, but has poor throughput
even prio is the default value.

Thanks,
Shaohua