cvs commit: src/sys/netinet ip_fw_pfil.c

[Simon 'corecode' Schubert]

On Friday, 10. December 2004 01:14, Andre Oppermann wrote:
> > >>>  Check that DUMMYNET_LOADED before seeking dummynet m_tag.
> > >>This change may be a mistake unless you can prove some significant
> > >>performance gain.
> > > Checking for DUMMYNET_LOADED is a simple pointer compare to NULL and
> > > doesn't add a memory write.  Not a big difference for sure but not
> > > hurting either.
> > If tag lookup cost becomes an important consideration in writing code
> > then we need to address that basic functionality.
> Actually this is a good argument and reasoning and I buy into it.  Not
> that is matter this much in this case but having nice and clean code
> wins big over time.  I've spent and am still spending too much time
> cleaning up old BSD PDP-11 "optimizations" and other shortcuts.

Forgive me if I'm way off here, I not experienced with the network stack as 
you are.

First of all I also think that this check here might be 
over(micro)optimization. Nevertheless, if tags appear to be a (small) 
performance hit, I conclude that there should be a fast way to check for the 
(possible?) existance of a tag. So for example having a bit field signaling 
the presence of the most important tags which are checked in the hot code 
path might help, so is this really stupid[tm]?

cheers
  simon

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