ref: 5fd2e746e1a2a00d2acbc0c3b1924b1ea22101e8
dir: /sys/src/9/teg2/notes/assumes-hz-under-1000/
./dat.h:9: #define MS2HZ (1000/HZ) /* millisec per clock tick */ ./random.c:87: addclock0link(randomclock, 1000/HZ); ../port/portclock.c:255: ms = 1000/HZ; ../port/portfns.h:335: #define TK2MS(x) ((x)*(1000/HZ))