[Bug 1337] SCP performance twice as slow as RCP

bugzilla-daemon at bugzilla.mindrot.org bugzilla-daemon at bugzilla.mindrot.org
Sat Jul 14 00:24:25 EST 2007


--- Comment #4 from Pádraig Brady <P at draigBrady.com>  2007-07-14 00:24:20 ---
Thanks for the reply Darren.

I understand about the trade off with compression :)
but the issue I think is due to buffer sizes,
and inappropriate sleeping. Have a look at
just 2 of the results again:

$ scp -C localhost:50MB_random /tmp
50MB_random                                   100%   50MB   4.6MB/s  

$ scp -C localhost:50MB_zeros /tmp
50MB_zeros                                    100%   50MB   2.3MB/s  

So compressing zeros (easy), and transfering much less data,
takes twice as long?

Looking a little bit deeper, shows that it only
uses 15% of the CPU while doing this! (11% for sshd and 4% for scp).
Note it's not waiting on the disk, because I tested
with a ram disk with the same results, like:

mount -t tmpfs tmpfs /mnt/rd
scp -C localhost:/mnt/rd/20MB /mnt/rd/20MB.copy

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