Re: lkwt in DragonFly

[David Rhodus <drhodus@xxxxxxxxxxx>]

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