Added a note on ssh connection reuse

This is a thing I that I always forget to say, but it is almost
necessary to get the real benefit of make -j with the current Makefile.
(The original plan was to batch per-node operations).

diff --git a/planetlab/exp-tool/Makefile.help b/planetlab/exp-tool/Makefile.help
index b046f29..d0f53cf 100644 (file)
--- a/planetlab/exp-tool/Makefile.help
+++ b/planetlab/exp-tool/Makefile.help
@@ -2,6 +2,21 @@ in almost all cases below it is recommended to use the -j option to make
 which was the point with uing make in the first place
 so that maximum degree of parallelism can be reached
 
 which was the point with uing make in the first place
 so that maximum degree of parallelism can be reached
 

+**********************************************************
+Note: to get the greatest speedup from make -j you should also enable
+connection reuse in your ssh setup, e.g., by having the following lines
+in your .ssh/config:
+host *
+       ControlMaster auto
+       ControlPath ~/.ssh/ssh_mux_%h_%p_%r
+       ControlPersist 4h
+
+Please note, however, that maximum concurrent per-node reuse is usually
+set to something low (typically 10), and this is a problem if some node
+in your topology has many links. In this case you should raise that limit
+on the slivers, or limit makefile concurrency (e.g., by using make -j10).
+**********************************************************
+

 ==================== usual target
 make [init+all]
         shortcut for 'make init all'
 ==================== usual target
 make [init+all]
         shortcut for 'make init all'