We stuck your change into devenv.c.  devproc.c was pretty bad too, since our
cpu servers often have upwards of 300 procs.  It was n**2 for ps which got
unwieldy for a tool rob is building, so we added a hash table to proc.c
to map pid to proctab slot.  Time for ps of our cpu servers goes from
4 seconds to milliseconds.  We'll include both changes in the next update
wrap.

We should probably rethink xxxgen, but for now we'll just speed up the
high runners; even the proc.c hash was only a few lines of code.

By the way, it's setting all the env's in your example that takes the
time, not forking in rc.  Rc doesn't reread the /env's.  If you
do an iostats on the example you'll see no opens of /env after
setting the vars:

% eval X^(`{seq 400})^('=1')
% echo /env/*|wc
      1     448    4443
% iostats rc
% rfork e
% time echo `{echo x | wc -c}
2
0.00u 0.00s 0.17r 	 echo 2
% ^D
read      157530 bytes, 9.022221 Kb/sec
write     95 bytes, 1.325316 Kb/sec
protocol  161425 bytes, 8.131304 Kb/sec
rpc       128 count

Message    Count   Low  High  Time Averg          in      out
clone         17     0     0     0     0 ms      119       85 bytes
walk          30     0   297  1092    36 ms      990      338 bytes
open           9    32   469  1142   126 ms       54      117 bytes
read          50     0 13593 17051   341 ms      750   157930 bytes
write          5     1    62    70    14 ms      175       35 bytes
clunk         14     0    16    31     2 ms       70       70 bytes
stat           2     0     1     1     0 ms       10      242 bytes
attach         1     0     0     0     0 ms      146       26 bytes

Opens    Reads  (bytes)   Writes  (bytes) File
    2        9    28100        0        0 /bin/echo
    1        3       36        0        0 (stdin)
    1        0        0        1        2 (stdout)
    1        0        0        4       93 (stderr)
    1        2      579        0        0 /rc/lib/rcmain
    1       23    87864        0        0 /bin/rc
    1        6    18680        0        0 /bin/time
    1        7    22271        0        0 /bin/wc
%