ref: 0c2cc473a7e0c6704a5a6a89019d62a67f6e5e82 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.; }