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Preliminary tests where actually not so good. Forgot to remove the java exclusions when using the jvisualvm CPU sampler. Majority of CPU time still within socketRead0[native] even after my buffer hack.
Also tried forcing setTcpNoDelay(false) as src/main/java/hudson/plugins/sshslaves/SSHLauncher.java sets connection.setTCPNoDelay(true).
Setting to false should reduce the number of packets and thus the amount of interrupts.
TCPNoDelay should mostly be used for interactive connections to get fast non piggybacked ACKs and not so good for bulk transfers as far as I understand. I find commit c2fcc257 in sshslaves to be contradictory to my understanding on how the TCP protocol works, but perhaps there are some cases in the real world where ACK piggybacking causes problems.
Did a simple "ifconfig ; sleep 3 ; ifconfig" while jenkins was transferring a big non-compressible mocked artifact, average RX packet size was about 1100 bytes.
SSH buffer size seems to be set to 4Mb in the sshslaves plugin:
src/main/java/hudson/plugins/sshslaves/SSHLauncher.java
private void expandChannelBufferSize(Session session, TaskListener listener) {
// see hudson.remoting.Channel.PIPE_WINDOW_SIZE for the discussion of why 1MB is in the right ball park
// but this particular session is where all the master/slave communication will happen, so
// it's worth using a bigger buffer to really better utilize bandwidth even when the latency is even larger
// (and since we are draining this pipe very rapidly, it's unlikely that we'll actually accumulate this much data)
int sz = 4;
m.invoke(session, sz*1024*1024);
I am using trilead-ssh2-build217-jenkins-3, sshslaves 1.6, Jenkins 1.554.1 with the bundled jetty container.