Reducing Startup Time

Step 1 -- stop loading Quicklisp

Despite its speed, scripting in Common Lisp usually have to face its startup time.

$ time fact.ros 10
Factorial 10 = 3628800
fact.ros 10  0.74s user 0.21s system 95% cpu 0.994 total

This very simple program took 0.74s to print the answer. Considering that all Common Lispers can easily compute the factorial of 10 in less than 1 sec, it is unbearably slow.

The first easy step to reduce the startup time is to skip loading Quicklisp, as it's not necessary for this program. Replace -Q flag by +Q in the ros command:

#!/bin/sh
#|-*- mode:lisp -*-|#
#|
-exec ros -Q -- $0 "$@"
+exec ros +Q -- $0 "$@"
|#

Retry time command to see how it worked:

$ time fact.ros 10
Factorial 10 = 3628800
-fact.ros 10  0.74s user 0.21s system 95% cpu 0.994 total
+fact.ros 10  0.57s user 0.19s system 97% cpu 0.780 total

It's mildly better.

Step 2 -- Making Executables (dump)

Roswell also provides a command to convert a script into an executable, ros build:

$ ros build fact.ros
[undoing binding stack and other enclosing state... done]
[saving current Lisp image into fact:
writing 4976 bytes from the read-only space at 0x20000000
writing 3168 bytes from the static space at 0x20100000
writing 52330496 bytes from the dynamic space at 0x1000000000
done]

It generates an executable named as fact. If your script doesn't have a file extension .ros, Roswell overrides your file and the behaviour is unknown.

Try time for the executable:

$ time fact 10
Factorial 10 = 3628800
-fact.ros 10  0.57s user 0.19s system 97% cpu 0.780 total
+fact 10  0.00s user 0.02s system 96% cpu 0.024 total

Well, is it fast enough now? :)

Step 3 -- disable core compression

ros build enables core compression by default in order to significantly reduce your binary size (from about 120MB to 30MB), but this adds a non-insignificant overhead to startup times of about 150ms.

Disable core compression with ros build --disable-compression <app.ros>.

There are several more options to ros build which are useful for reducing the binary size (with less reliability). Note that they are not useful for making the startup time faster, though: They are only useful for reducing the binary size. See man ros-build for the detailed usage.