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    SubjectRe: getdents - ext4 vs btrfs performance
    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


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