On Sun, Aug 22, 2010 at 10:31:55PM +0300, Avi Kivity wrote:
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?
You're absolutely right -- I forget that it's a fast ethernet switch :-)
>$ 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.
Rich.
--
Richard Jones, Virtualization Group, Red Hat
http://people.redhat.com/~rjones
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