Subject: Re: "const int" in conf/param.c?
To: None <>
From: Simon Burge <>
List: tech-kern
Date: 04/25/1999 22:55:17
A few people have commented on why not leave msize and mclbytes in
conf/param.c as plain old patchable ints.  Part of the reason was the
comment preceding the variables:

	 * Actual network mbuf sizes (read-only), for netstat.

These two variables aren't used anywhere in the kernel.

So I looked a bit further ... here's how each arch defines MSIZE and

	alpha	def  256	cond 1<<11
	arm32	def  128	def  1<<11
	bebox	def  128	def  1<<11
	i386	def  128	cond 1<<11
	m68k	def  128	cond 1<<11
	macppc	def  128	def  1<<11
	news	def  128	conf 1<<11
	ofppc	def  128	def  1<<11
	pc532	cond 128	cond 1<<11
	pica	def  128	def  1<<11 (but gets MCLSHIFT wrong)
	pmax	def  128	cond 1<<11
	powerpc	def  128	def  1<<11
	sparc	def  128	def  1<<11
	sparc64	def  128	def  1<<11
	vax	cond 128	cond 1<<11

Two questions arise from this:

 + Why does the alpha want 256 byte mbufs?  If the 64 bit architecture
   is really an issue, should sparc64 also have 256 byte mbufs?

 + Modulo the alpha mbuf size issue, should we move the default setting
   of MSIZE and MCLBYTES to sys/param.h?  We can have:

	#ifndef MSIZE
	#define MSIZE ...
	#ifndef MCLSHIFT
	#define MCLSHIFT ...
	#define MCLBYTES (1 << MCLSHIFT)

   and each port can override this if it wants to in machine/param.h if
   it really wants to.

So, is there any real-world use for ever changing these sizes?

Along the same issue, there seems at first glance to be a lot in the
various machine/*.h files that is needlessly duplicated.  Is it worth
the effort to clean all this up?