Tool to measure ssh latency ("sshping") ?

[Philipp Marek]

> while true
> do
> time echo test | ssh user at machine.somewhere 
> <mailto:user at machine.somewhere> cat
> done

Well, shouldn't it be more like this?

   while true
   do
     echo foobar
   done | ssh user at machine > /dev/null


> But for a remote rpc service that requires low latency, take a look
> at multiplexing
> https://en.wikibooks.org/wiki/OpenSSH/Cookbook/Multiplexing and
> daemonize the Master connection

Yeah, that keeps a common SSH connection as well.



My €0.02: just use existing tools.

   for nr in $(seq 0 3600)
   do
     id=$(date +%s.%N,$$,$nr | md5sum)
     echo $id
     sleep 1
   done | strace -o /tmp/ssh.trace -tt -s 30 --trace=read,write > 
/dev/null

Please note that "strace" does a dup() of STDIN, STDOUT, and STDERR,
so it's not fd 0,1,2 but 4,5,6 for me.


Sadly I couldn't get strace to log _only_ these fd --
but but by associating the read() and write() requests by the MD5-ID
it should be fairly easy to associate the matching calls,
and subtracting the timestamps should get a fairly accurate picture
of the latency.

(Also you should be able to see the communication to/from the ssh
process vs. the communication of ssh to the other host - ie. you can
measure "input encryption time, latency to remote answer, output
decryption time".)

That doesn't include processing _outside_ ssh, of course.


If the machine you're doing that on has a fairly recent linux kernel
running, you could also use bpftrace to get better filtered results.