Re: Please do not yell at people for trying to help you.

[Eduardo Horvath <eeh%NetBSD.org@localhost>]

On Fri, 12 Nov 2010, Thor Lancelot Simon wrote:

> The claim that NetBSD only cares about x86 is even more absurd.  NetBSD
> supports a huge array of architectures, usually in both their modern and
> ancient implementations.  We'll run on everything from R2000 to the newest
> multicore 64-bit MIPS processors; a similar range of support exists for
> ARM, powerpc, and many other processor and system families.  We have not
> done as good a job keeping up with SPARC or the death-rattle models of 68k
> but we certainly haven't ripped SPARC or 68k support out either -- nor does
> anyone intend to do so.

While support for other platforms are not being dropped, there does seem 
to be an implicit assumption that everyone is running on x86 (or more 
specifically amd64) and code should be optimized for performance on that 
architecture.  Even "modern" architectures that are not amd64 are 
suffering.

Take, for example, the simple act of byte swapping network data.  x86 has 
a bswap instruction.  SPARC and PowerPC architectures have a multiplexer 
on the load/store.  (Don't know about MIPS, don't remember about ARM.)  In 
order to swap a 64-bit value in registers you need to issue a series of 
shift, mask, and or instrutions, usually about 8 of them, most of which 
are depenent (cannot be issued in parallel on a superscalar machine).
The macro NetBSD uses here is bswap64().  This maps very well to the x86 
instruction, but is really not usable for any machine that does the 
swapping in the load/store path.  Instead we could use something like 
load_be64()/load_le64()/store_be64()/store_le64() which could be mapped to 
a reverse-endian load/store instruction on architetures that support it 
and bswap on x86.  

Instead, in most cases, things that are not x86 need to jump though hoops 
to pretend to be x86.  At least that't the way things look to me.

BTW, I'm trying very hard not to yell and keep hyperbole to a minimum.

Eduardo