On 08/22/2010 10:02 PM, Richard W.M. Jones wrote:
> Interesting, I'd have guessed that encryption will dominate the cpu
> cost, and that compression would be a win since there's less to
> encrypt and transmit.
Maybe my explanation is wrong too. virt-p2v was definitely much
slower when we added the '-C' option. However read on.
I just ran a test again on my local LAN. This is between two
approximately equal Fedora machines, over a moderate quality consumer
gigabit ethernet switch. The command approximates what virt-p2v does:
sending 1MB blocks from local /dev device, and at the target end using
cat to write to a file.
$ time sh -c 'dd bs=1M if=/dev/vg_trick/Windows7x64 | ssh amd "cat>
/tmp/copy1"'
16384+0 records in
16384+0 records out
17179869184 bytes (17 GB) copied, 1473.26 s, 11.7 MB/s
real 24m33.269s
user 4m16.944s
sys 4m43.181s
11.7 MB/s = 93.6 Mb/s. Not the cpu is not loaded. Are you sure you're
using 1GbE here?
$ time sh -c 'dd bs=1M if=/dev/vg_trick/Windows7x64 | ssh -C amd
"cat> /tmp/copy2"'
16384+0 records in
16384+0 records out
17179869184 bytes (17 GB) copied, 1412.7 s, 12.2 MB/s
real 23m32.736s
user 17m52.739s
sys 5m0.884s
Suddenly you're cpu bound. So it looks like compression is really
expensive for some reason.
--
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.