Laptops and busy wait

[Neil Toronto]

For no good reason, I'm developing on a laptop running Linux. Quake 3 
presents it with a special problem: even with com_maxfps set, it runs 
busy wait loop, which eats up CPU (near 100%), which turns on frequency 
throttling (or scaling), which lowers the framerate.

I don't recall having this problem when I was developing mods on 
Windows. (However, looking through the engine source, I can't see a good 
reason it wouldn't have done it there.)

The busy wait loop is in common.c:

do {
    <call event processing loop>
    ...
} while (msec < minMsec);

Possible solution:

do {
    <call event processing loop>
    ...
    if (msec < minMsec) Sys_Sleep(0);
} while (msec < minMsec);

This kicks Quake 3 off the scheduler if the frame didn't take long 
enough, so the CPU is free to pause for a half millisecond and cool off. 
Sys_Sleep() is a new function in unix_shared.c and win_shared.c. On unix 
systems it calls usleep(msec * 1000), on Windows, Sleep(msec). On both 
systems, Sys_Sleep(0) behaves the same way.

I don't know what this would do when a server is running. My own 
codebase is heavily modified - no server, no netcode, etc. It works fine 
with just a client game, though.

Thoughts?

Neil