ref: 11b5c4b8bf0a15777e9a7f2292f6c80f5a7b4a2d dir: /sys/src/cmd/2l/cputime.c/
double cputime(void) { long t[4]; long times(long*); int i; times(t); for(i=1; i<4; i++) t[0] += t[i]; return t[0] / 100.; }