SSH and performance overhead

One of the first things I do when I come home – I open a port on the router with upnpc, log into my office's PC and set up a reverse ssh connection to my notebook, then I use sshfs to mount the remote filesystem.

I know that ssh uses encryption (thanks, Cap) and that comes at the price of CPU time. I guess, modern CPUs have instructions to accelerate encryption.

What's the price?

So, let's begin the experiment

$ dd if=/dev/urandom of=bigfile bs=8M count=50

gives me a big (400M) file. By the way, it took 107.675 s (3.9 MB/s) on i7-2630QM (only 1 core was loaded).

Let's just read it. First time, after a reboot:
$ dd if=bigfile of=/dev/null bs=8M
50+0 records in
50+0 records out
419430400 bytes (419 MB) copied, 1.7027 s, 246 MB/s

Consecutive runs:
$ dd if=bigfile of=/dev/null bs=8M
50+0 records in
50+0 records out
419430400 bytes (419 MB) copied, 0.0819643 s, 5.1 GB/s

Let's read that via ssh:
$ sudo sshfs -o allow_other,uid=1000 user@localhost:/home/user/ /home/user/self/
$ dd if=self/bigfile of=/dev/null bs=8M
50+0 records in
50+0 records out
419430400 bytes (419 MB) copied, 6.985 s, 60.0 MB/s

The same experiment, on an old AMD Athlon(tm) 64 Processor 3000+ (1 Ghz): 38.663 s, 10.8 MB/s

Ok, here is the price.