From owner-freebsd-net  Thu Oct 11 11:42:36 2001
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Date: Thu, 11 Oct 2001 11:42:30 -0700 (PDT)
From: Matthew Jacob <mjacob@feral.com>
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To: Luigi Rizzo <rizzo@aciri.org>
Cc: <freebsd-net@FreeBSD.ORG>
Subject: Re: review of change to bridge.h
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Maybe bcmp is right. I believe having IS_ETHER_BROADCAST is too
useful a macro....


On Thu, 11 Oct 2001, Luigi Rizzo wrote:

> >
> >
> > On Thu, 11 Oct 2001, Luigi Rizzo wrote:
> >
> > > I guess it might be marginally more efficient to
> > > call bcmp() (and rely on it being optimized), or do 3
> > > comparisons with unsigned short *
> > >
> > > > +#define      IS_ETHER_BROADCAST(a) ( \
> > > > +     ((unsigned short *)(a))[0] == 0xffff && \
> > > > +     ((unsigned short *)(a))[1] == 0xffff && \
> > > > +     ((unsigned short *)(a))[2] == 0xffff)
> >
> > You can't assume a short * is aligned either.
>
> well, in this case a is always on
> an even boundary, but whether this is also a multiple of 4
> is very driver-specific.
>
> Anyways, feel free to commit whatever version you prefer -- it
> is better than the current code anyways.
>
> I would probably use bcmp... i find myself trying to rely
> more and more on compiler optimizations, because the hand
> optimization that we all liked to do in the early years are
> very architecture specific and tend to become bad ideas as
> architectures evolve.
>
> There are parts of the code (e.g. in mbuf handling) where "optimized"
> versions of some routines (e.g. m_copym vs. m_copypacket) save
> maybe a couple of jumps/calls at the price of 500-1000 bytes of
> extra code (and associated cache pollution).
>
> 	cheers
> 	luigi
> ----------------------------------+-----------------------------------------
>  Luigi RIZZO, luigi@iet.unipi.it  . ACIRI/ICSI (on leave from Univ. di Pisa)
>  http://www.iet.unipi.it/~luigi/  . 1947 Center St, Berkeley CA 94704
>  Phone: (510) 666 2927
> ----------------------------------+-----------------------------------------
>


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