MSTOHZ(9) Kernel Developer's Manual MSTOHZ(9)

mstohz, hztoms
convert between milliseconds and system clock ticks

#include <sys/param.h>

unsigned int
mstohz(unsigned int ms);

unsigned int
hztoms(unsigned int hz);

The mstohz() macro can be used to convert time in milliseconds to system clock ticks, as used by the callout(9) facility, in an integer-overflow safe way. Conversely, hztoms() converts system clock ticks to milliseconds.

These macros are defined in the ⟨sys/param.h⟩ header. Individual ports can have a processor-specific, more efficient version implemented in their ⟨machine/param.h⟩ header as a define.

The return value is either the number of clock ticks or milliseconds for the specified value.

param(3), callout(9), tvtohz(9)

Neither mstohz() nor hztoms() make use of expensive 64-bit integer arithmetic. The result from mstohz() will be rounded down to one second if the parameter is larger than 131072 milliseconds.
September 28, 2019 NetBSD 10.0