Re: [PKT_SCHED]: Add stateless NAT

David Miller wrote:

From: jamal <redacted>
Date: Thu, 27 Sep 2007 08:39:45 -0400

quoted

quoted

+config NET_ACT_NAT
+        tristate "Stateless NAT"
+        depends on NET_CLS_ACT
+        select NETFILTER

I am gonna have to agree with Evgeniy on this Herbert;->
The rewards are it will improve performance for people who dont need
netfilter.

I agree that we should move the functions out.   However...

You have to realize that this logic is a complete crock
of shit for %99.99999999999999999999 of Linux users out there
who get and only use distribution compiled kernels which are
going to enable everything anyways.

So we better make sure there are zero performance implications at some
point just for compiling netfilter into the tree.  I know that isn't
the case currently, but that means that we aren't helping out the
majority of Linux users and are thus only adding these optimizations
for such a small sliver of users and that is totally pointless and
sucks.

The hooks themselves actually shouldn't be that much of a problem
since without any registered users they come down to a simple
list_empty check. The bigger problem is probably the fact that
the "okfn" is usually declared inline, but we also take its address
for nf_hook_slow, so at least with forced inlining, we end up
with one inlined and one out-of-line version.

Looking at ip_input.o as example (everything without forced inlining):

   text    data     bss     dec     hex filename
   2076       8       0    2084     824 net/ipv4/ip_input.o
   3483       8       0    3491     da3 net/ipv4/ip_input.o


So we have roughly 1.75 more code for the two hooks. For reference,
without using the function pointer it increases a lot less:

   text    data     bss     dec     hex filename
   2319       8       0    2327     917 net/ipv4/ip_input.o

similar with not inlining ip_rcv_finish() and ip_local_deliver_finish():

   text    data     bss     dec     hex filename
   2282       8       0    2290     8f2 net/ipv4/ip_input.o

Any ideas how to do this better? Unforunately we need the function
pointers for reinjecting queued packets ..