On Fri, 20 Jul 2007, Lennart Sorensen wrote:
On Fri, Jul 20, 2007 at 09:58:50AM -0400, Justin Piszcz wrote:
I have a multi-core Q6600 CPU on a 10-disk Raptor RAID 5 running XFS.
I just pulled down the Debian Etch 4.0 DVD ISO's, one for x86 and one for
x86_64, when I ran md5sum -c MD5SUMS, I see ~280-320MB/s. When I ran the
second one I see upwards of what I should be seeing 500-520MB/s.
NOTE:: These MD5 contain the 3 DVD ISO's for each platform, 6 total ISOs.
I know md5sum is cpubound to a degree, do you think that is what is
happening here? Each core can only sustain ~300MB/s and then with two of
four cores working, it can exceed that amount or is there some similarity
with RAID1 in linux compared to RAID5?
With RAID1, if you use a single read thread, you will get 60-70MB/s read
on a dual raptor raid1. If you use two(?) or three threads, it will read
from both disks and you will see 120-140MB/s.
Is there some commonality with software RAID1 and RAID5 in Linux in this
regard?
Could you just run top while doing md5sum and see how much cpu md5sum is
using on the cpu it is on? After all if it says 100% for the process,
then yes it is cpu bound at 300MB/s, and if not then I guess there has
to be another explanation.
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
679 abc 23 0 4092 512 432 R 92 0.0 0:02.77 md5sum
$ /usr/bin/time md5sum debian-40r0-i386-DVD-1.iso
79f5bcbb36335e14142fc3578b1de96e debian-40r0-i386-DVD-1.iso
10.69user 3.52system 0:14.47elapsed 98%CPU (0avgtext+0avgdata 0maxresident)k
0inputs+0outputs (1major+205minor)pagefaults 0swaps
Looks like it.
It looks pretty likely, since I just tried running md5sum on a 130MB
file here, and it takes 0.444s of user cpu time and 0.068s of system
time to process, and I ran it multiple times so the file ended up cached
in ram so disk speed isn't a concern, which I figure means my system
runs md5sum at about 250MB/s. This is on a single core Athlon 64 3500+
(2.2GHz). So if you have a slightly faster as you do with a 2.4GHz Core
2, then 300MB/s seems perfectly reasonable per core. I don't quite know
how md5 hashes work, but I really doubt they are something you are
likely to be able to make threaded.
--
Len Sorensen
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