[Users] Curious about ploop performance results.
Kir Kolyshkin
kir at openvz.org
Sat May 3 11:31:44 PDT 2014
On 05/02/2014 04:38 PM, jjs - mainphrame wrote:
> Thanks Kir, the /dev/zero makes sense I suppose. I tried with
> /dev/random but that blocks pretty quickly - /dev/urandom is better,
> but still seems to be a bottleneck.
You can use a real file on tmpfs.
Also, in general, there are very many factors that influence test
results. Starting from the cron jobs and other stuff (say, network
activity) that runs periodically or sporadically and spoils your
results, to the cache state (you need to use vm_drop_caches, or yet
better, reboot between tests), to the physical place on disk where your
data is placed (rotating hdds tend to be faster at the first sectors
compared to the last sectors, so ideally you need to do this on a clean
freshly formatted filesystem). There is much more to it, can be some
other factors, too. The rule of thumb is results need to be reproducible
and explainable.
Kir.
>
> As for the dbench results, I'd love to hear what results others obtain
> from the same test, and/or any other testing approaches that would
> give a more "acceptable" answer.
>
> Regards,
>
> J J
>
>
>
> On Fri, May 2, 2014 at 4:01 PM, Kir Kolyshkin <kir at openvz.org
> <mailto:kir at openvz.org>> wrote:
>
> On 05/02/2014 03:00 PM, jjs - mainphrame wrote:
>> Just for kicks, here are the data from the tests. (these were run
>> on a rather modest old machine)
>>
>>
>>
>> Here are the raw dbench data:
>>
>>
>> #clients vzhost simfs CT ploop CT
>> ---------------------------------------------------------------------
>> 1 11.1297MB/sec 9.96657MB/sec 19.7214MB/sec
>> 2 12.2936MB/sec 14.3138MB/sec 23.5628MB/sec
>> 4 17.8909MB/sec 16.0859MB/sec 45.1936MB/sec
>> 8 25.8332MB/sec 22.9195MB/sec 84.2607MB/sec
>> 16 32.1436MB/sec 28.921MB/sec 155.207MB/sec
>> 32 35.5809MB/sec 32.1429MB/sec 206.571MB/sec
>> 64 34.3609MB/sec 29.9307MB/sec 221.119MB/sec
>
> Well, I can't explain this, but there's probably something wrong
> with the test.
>
>
>>
>> Here is the script used to invoke dbench:
>>
>> HOST=`uname -n`
>> WD=/tmp
>> FILE=/usr/share/dbench/client.txt
>>
>> for i in 1 2 4 8 16 32 64
>> do
>> dbench -D $WD -c $FILE $i &>dbench-${HOST}-${i}
>> done
>>
>> Here are the dd commands and outputs:
>>
>> OPENVZ HOST
>> ----------------
>> [root at vzhost ~]# dd bs=1M count=512 if=/dev/zero of=test
>> conv=fdatasync
>> 512+0 records in
>> 512+0 records out
>> 536870912 bytes (537 MB) copied, 11.813 s, 45.4 MB/s
>> [root at vzhost ~]# df -T
>> Filesystem Type 1K-blocks Used Available Use% Mounted on
>> /dev/sda2 ext4 20642428 2390620 17203232 13% /
>> tmpfs tmpfs 952008 0 952008 0% /dev/shm
>> /dev/sda1 ext2 482922 68436 389552 15% /boot
>> /dev/sda4 ext4 51633780 3631524 45379332 8% /local
>> [root at vzhost ~]#
>>
>>
>> PLOOP CT
>> ----------------
>> root at vz101:~# dd bs=1M count=512 if=/dev/zero of=test conv=fdatasync
>> 512+0 records in
>> 512+0 records out
>> 536870912 bytes (537 MB) copied, 2.50071 s, 215 MB/s
>
> This one I can explain :)
>
> This is caused by ploop optimization that was enabled in the
> kernel recently.
> If data block is all zeroes, it is not written to the disk (same
> thing as sparse files,
> just for ploop).
>
> So you need to test it with some real data (anything but not all
> zeroes).
> I am not sure how fast is /dev/urandom but this is one of the options.
>
>>
>> root at vz101:~# df -T
>> Filesystem Type 1K-blocks Used Available Use%
>> Mounted on
>> /dev/ploop11054p1 ext4 4539600 1529316 2804928 36% /
>> none devtmpfs 262144 4 262140 1% /dev
>> none tmpfs 52432 52 52380 1% /run
>> none tmpfs 5120 0 5120 0% /run/lock
>> none tmpfs 262144 0 262144 0% /run/shm
>> root at vz101:~#
>>
>>
>> SIMFS CT
>> ----------------
>> root at vz102:~# dd bs=1M count=512 if=/dev/zero of=test conv=fdatasync
>> 512+0 records in
>> 512+0 records out
>> 536870912 bytes (537 MB) copied, 12.6913 s, 42.3 MB/s
>> root at vz102:~# df -T
>> Filesystem Type 1K-blocks Used Available Use% Mounted on
>> /dev/simfs simfs 4194304 1365500 2828804 33% /
>> none devtmpfs 262144 4 262140 1% /dev
>> none tmpfs 52432 52 52380 1% /run
>> none tmpfs 5120 0 5120 0% /run/lock
>> none tmpfs 262144 0 262144 0% /run/shm
>> root at vz102:~#
>>
>> Regards,
>>
>> J J
>>
>>
>>
>>
>> On Fri, May 2, 2014 at 2:10 PM, jjs - mainphrame
>> <jjs at mainphrame.com <mailto:jjs at mainphrame.com>> wrote:
>>
>> You know the saying, "when something seems too good to be
>> true"...
>>
>> I just installed centos 6.5 and openvz on an older machine,
>> and when I built an ubuntu 12.04 CT I noticed that ploop is
>> now the default layout. Cool. So I built another ubuntu12.04
>> CT, identical in every way except that I specified smifs, so
>> I could do a quick performance comparison.
>>
>> First I did a quick timed dd run, then I ran dbench with
>> varying numbers of clients.
>>
>> The simfs CT showed performance roughly similar to the host,
>> which was not too surprising.
>> What did surprise me was that the ploop CT showed performance
>> which was significantly better than the host, in both the dd
>> test and the dbench tests.
>>
>> I know someone will tell me "dbench is a terrible benchmark"
>> but it's also a standard. Of course, if anyone knows a
>> "better" benchmark, I'd love to try it.
>>
>> Regards,
>>
>> J J
>>
>>
>>
>>
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