* Tobias C Rittweiler [2010-06-27 05:39] writes:

Compiling swank.lisp via

(time (compile-file "swank.lisp"))

vs

(time (compile-file "swank.lisp" :verbose nil :print nil))

reveals a major overhead.

First command takes ~14secs, whereas the second 2.3 secs.

The first command at the terminal, without Slime, takes roughly 5.5 secs.

Using :spawn, without dedicated output stream. Dedicated output stream probably has a much better performance, but where does /that/ much overhead come from in the default implementation?

COMPILE-FILE with *COMPILE-PRINT* flushes the output buffer very often that means that lots of small messages are sent. With :spawn each message is first sent to the control thread than through the printer to the socket; Emacs needs to parse it and copy it to another buffer. So lots of copying&garbage collecting and the encoding is also not efficient for this use; but there is also plenty of room for the OS kernel to make bad scheduling decisions. On Linux the situation seems to be bad when the Lisp process produces output at about the same rate that Emacs can consume; the overhead is much less if the Lisp process is faster than that or if Emacs gets slower (inserting an artificial delay on the Emacs side can reduce the overhead). That's my hypothesis anyway; it's hard to measure those things.

Sending lots of small messages will never be efficient. The only cure would be to add a buffer somewhere to reduce the number of messages; possibly combined with a timeout.

Helmut