Optimising Speed 2 (time)

• Strip asserts and other instrumentation for release

• Push work to other/bigger machines

• Pick unbalanced algorithms harder on server, easier on embedded system

• Minimise heap use: it is still slow!

• Reduce interface crossing such as in OS calls: usually slow.

• Avoid copying data

• Avoid cache-unfriendly stride and indirection

• Get thread (and interrupt) priorities right

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EXAMPLE: Assert stripping (and eliminating debug support) typically halves size of many applications.

CHECKLIST:

• Are you sure that your asserts don’t have side-effects that will break your program when stripped? They should never have any side effect other than to stop the application immediately if something is manifestly wrong.

• When handling significant quantities of data in arrays, in C/C++/Java increment the rightmost index in the inner loop.

• Are you copying data you can avoid? Early OS implementations wasted more than half their CPU cycles copying.

• Are you getting thread priorities right? Avoid starvation. Make sure User Interface and other real-time activity including I/O gets handled promptly.