On Fri, Mar 09, 2012 at 12:29:29PM +0100, Lukas Czerner wrote:

Hi,

I have created a simple script which creates a bunch of files with
random names in the directory and then performs operation like list,
tar, find, copy and remove. I have run it for ext4, xfs and btrfs with
the 4k size files. And the result is that ext4 pretty much dominates the
create times, tar times and find times. However copy times is a whole
different story unfortunately - is sucks badly.

Once we cross the mark of 320000 files in the directory (on my system) the
ext4 is becoming significantly worse in copy times. And that is where
the hash tree order in the directory entry really hit in.

Here is a simple graph:

http://people.redhat.com/lczerner/files/copy_benchmark.pdf

Here is a data where you can play with it:

https://www.google.com/fusiontables/DataSource?snapid=S425803zyTE

and here is the txt file for convenience:

http://people.redhat.com/lczerner/files/copy_data.txt

I have also run the correlation.py from Phillip Susi on directory with
100000 4k files and indeed the name to block correlation in ext4 is pretty
much random :)

_ext4_
Name to inode correlation: 0.50002499975
Name to block correlation: 0.50002499975
Inode to block correlation: 0.9999900001

_xfs_
Name to inode correlation: 0.969660303397
Name to block correlation: 0.969660303397
Inode to block correlation: 1.0


So there definitely is a huge space for improvements in ext4.

Thanks Lukas, this is great data.  There is definitely room for btrfs to
speed up in the other phases as well.

-chris