On 13/03/10 03:05, Shridhar Daithankar wrote:
Hi,
Just wanted to share an interesting experience I had today.
Check http://ghodechhap.net/btrfs.performance.txt
Maybe you're looking for http://docs.python.org/library/filecmp.html
One cannot help but think that you took a disk-bound process and turned
it into a cpu-bound one. Since you're just interested in which files are
different you should have just used `cmp` instead of `md5sum`
the latter is just overkill and I'd assume calling an external command
that many times can't be very nice either.
here are some comparisons, they use /usr/lib - i figured 75000 files
should be a good test... I made this as deliberately
unfair/in-comparable as possible, I wanted to show the potential
overhead of calling md5sum that many times.
[[ky] ~]# }} time python -c "import filecmp; print
len(filecmp.dircmp('/usr/lib', '/temp/lib').diff_files)"
80
real 2m24.240s
user 0m10.123s
sys 0m10.669s
That looks reasonable, on this crappy 5400 rpm (sata) laptop harddisk
with ext4.
You'll note that test below is pretty much just to see how much time
calling md5sum takes, /tmp/a is a 1 byte file(contains the character a,
to give md5sum as simple a job as possible). /tmp is a tmpfs, not that
it matters as /tmp/a most likely remains in cached the entire time
[[ky] ~]# }} time find /temp/lib -type f | wc -l
75272
real 0m0.532s
user 0m0.140s
sys 0m0.383s
[[ky] ~]# }} time find /temp/lib -type f -exec md5sum /tmp/a \;
real 2m6.781s
user 0m2.200s
sys 0m15.409s
the disk-status light didn't come on at all during those 2mins meanwhile
I could hear my cpu-fan going crazy the whole time (1.6ghz). I should
note, the light remained on the entire time during the filecmp and cpu
stayed low(800mhz) for most of that time as well.
