MAKEIPL
#define IPL_SOFTCLOCK MAKEIPL(1) /* timeouts */
#define IPL_SOFTNET MAKEIPL(2) /* protocol stacks */
#define IPL_BIO MAKEIPL(3) /* block I/O */
#define IPL_NET MAKEIPL(4) /* network */
#define IPL_SOFTTTY MAKEIPL(5) /* delayed terminal handling */
#define IPL_TTY MAKEIPL(6) /* terminal */
#define IPL_VM MAKEIPL(7) /* memory allocation */
#define IPL_AUDIO MAKEIPL(8) /* audio */
#define IPL_CLOCK MAKEIPL(9) /* clock */
#define IPL_HIGH MAKEIPL(10) /* everything */
#define IPL_IPI MAKEIPL(11) /* interprocessor interrupt */