"git submodule foreach" very slow ...

git usually is lightning fast, it even knows how many processor
threads are available and uses them. for a test i converted
https://gar.svn.sourceforge.net/svnroot/gar/csw/mgar/pkg into a git
repository with one subrepository for every directory. rebasing takes
now 3 hours, while git without subrepositories takes 10 minutes.

$ ls -1 | wc
   1162    1162    9527
$ time git submodule foreach git svn rebase
....
real    199m29.626s
user    60m49.631s
sys     70m51.888s

contrary, if one creates one git repository for all these little
directories, rebasing is twenty times faster:
$ time git svn rebase
...
real    10m1.032s
user    5m33.632s
sys     2m53.955s

rupert