lkwt in DragonFly

[David Rhodus]

On Feb 8, 2004, at 7:01 PM, Matthew Dillon wrote:

    You should also check the critical section API overhead in 
FreeBSD-5.
    If it is a subroutine call and if it actually disables interrupts
    physically, the overhead is going to be horrendous... probably 
similar
    to the overhead of a mutex (sti and cli are very expensive 
instructions).
    In DFly the critical section code is only two or three 'normal' 
inlined
    instructions and does not physically disable interrupts.
On a P4 with the sti/cli instruction pair, your looking at ~300 cycles.
But on an AMD64 your only looking at the overhead of ~20 cycles.
-DR