Re: dm-ioband: Test results.

[Vivek Goyal <vgoyal@redhat.com>]

On Thu, Apr 16, 2009 at 10:11:39PM -0400, Vivek Goyal wrote:
> On Thu, Apr 16, 2009 at 04:57:20PM -0400, Vivek Goyal wrote:
> > On Mon, Apr 13, 2009 at 01:05:52PM +0900, Ryo Tsuruta wrote:
> > > Hi Alasdair and all,
> > > 
> > > I did more tests on dm-ioband and I've posted the test items and
> > > results on my website. The results are very good.
> > > http://people.valinux.co.jp/~ryov/dm-ioband/test/test-items.xls
> > > 
> > > I hope someone will test dm-ioband and report back to the dm-devel
> > > mailing list.
> > > 
> > 
> 
> Ok, one more test. This time to show that with single queue and FIFO
> dispatch a writer can easily starve the reader.
> 
> I have created two partitions /dev/sda1 and /dev/sda2. Two ioband devices
> ioband1 and ioband2 on /dev/sda1 and /dev/sda2 respectively with weights
> 40 and 20.
> 
> I am launching an aggressive writer dd with prio 7 (Best effort) and a
> reader with prio 0 (Best effort).
> 
> Following is my script.
> 
> ****************************************************************
> rm /mnt/sdd1/aggressivewriter
> 
> sync
> echo 3 > /proc/sys/vm/drop_caches
> 
> #launch an hostile writer
> ionice -c2 -n7 dd if=/dev/zero of=/mnt/sdd1/aggressivewriter bs=4K count=524288 conv=fdatasync &
> 
> # Reader
> ionice -c 2 -n 0 dd if=/mnt/sdd1/testzerofile1 of=/dev/null &
> wait $!
> echo "reader finished"
> **********************************************************************

More results. Same reader writer test as above, the only variation I 
have done is change the class of reader to RT from BE.

ionice -c 1 -n 0 dd if=/mnt/sdd1/testzerofile1 of=/dev/null &

Even chaning the class of reader does not help. Writer still starves the
reader.

Without dm-ioband
=================
First run
2147483648 bytes (2.1 GB) copied, 43.9096 s, 48.9 MB/s (Reader)
reader finished
2147483648 bytes (2.1 GB) copied, 85.9094 s, 25.0 MB/s (Writer)

Second run
2147483648 bytes (2.1 GB) copied, 40.2446 s, 53.4 MB/s (Reader)
reader finished
2147483648 bytes (2.1 GB) copied, 82.723 s, 26.0 MB/s (Writer)

With dm-ioband
==============
First run
2147483648 bytes (2.1 GB) copied, 69.0272 s, 31.1 MB/s (Writer)
2147483648 bytes (2.1 GB) copied, 89.3037 s, 24.0 MB/s (Reader)
reader finished

Second run
2147483648 bytes (2.1 GB) copied, 64.8751 s, 33.1 MB/s (Writer)
2147483648 bytes (2.1 GB) copied, 89.0273 s, 24.1 MB/s (Reader)
reader finished

Thanks
Vivek