Re: [PATCH 4/7] mac80211: make ieee80211_get_hdrlen_from_skb return unsigned

Pavel Roskin
2008-06-06T20:15:58Z

On Fri, 2008-06-06 at 11:47 -0700, Harvey Harrison wrote:

> unlikely() isn't some magic make-me-faster function, it just moves co=
de
> to the end of the function to get it out of the icache and jumps to i=
t
> in the unlikely case it is taken. When all there is is a return, I
> don't think it even makes any difference. In both these cases a comm=
ent
> is probably more appropriate.

If we don't more return to the end, we get something like:

compare skb->len to 10
if more or equal goto 1
return
1: <the likely case>

=EF=BB=BFI don't know much about modern processor design, but I remembe=
r reading
that even a very short jump would flush the instruction pipeline and
cause some delay.

I would keep unlikely() and let the compiler think what to do with it.

--=20
Regards,
Pavel Roskin
--
To unsubscribe from this list: send the line "unsubscribe linux-wireles=
s" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html