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From: jgd@cix.co.uk (John Dallman)
Newsgroups: comp.arch
Subject: Re: Computer architects leaving Intel...
Date: Fri, 30 Aug 2024 15:48 +0100 (BST)
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In article <2024Aug30.122638@mips.complang.tuwien.ac.at>,
anton@mips.complang.tuwien.ac.at (Anton Ertl) wrote:

> AMD64 already has the buy-in of application vendors for desktops and
> servers, so it does not have the problem that extensions create
> uncertainty among application vendors.
> 
> My guess is that there are the following motivations:
> 
> 1) The new instructions make technical sense (for certain
> applications).

This is sometimes true, but manufacturers tend to over-promote them,
claiming wider applicability and bigger effects than show up in real
application code. After a few disappointments, ISVs tend to become less
keen on doing work on marketing advice. 

Some manufacturers pay bonuses to their technical marketing people for
getting ISVs to adopt new ISA extensions. This is counter productive,
because it means the ISVs are sure that the marketing advice will take no
account of their interests. 

They prefer to wait until an extension has been out for several years
before supporting it, so that it's available in pretty well all the
end-user hardware that hasn't finished its depreciation yet. That's
driven by a facet of the application software industry that most hardware
manufacturers don't seem to understand. They appear to assume that
computers are set up with an initial software load and carry on running
that for their entire lives. 

In fact, organisations replace about a quarter of their machines each
year, always buying up-to-date ones, and want to run the /same/ version
of software on all of them. They want common software versions for data
compatibility, ease of training and so on. That means that a new release
of an application has to run on all the machines sold in the last four
years, sometimes longer. 

Some manufacturers expect ISVs to produce multiple versions of software
for different sets of ISA extensions. They'll do that if the gains are
large enough, but they have to be quite large: for my employer, 25% is
enough, but 10% isn't. We haven't had to make a decision in between those
numbers yet. We've had one 25% case, for Intel SSE2, and many of 10% or
less. 

> 2) Even if the applications that the users use don't benefit from 
> the extensions, the users think (thanks also to Intels marketing) 

The sheer flood of extensions from Intel means most end-user
organisations have stopped trying to keep track these days. 

John