By Tony Smith
18th April 2006 10:27 GMT
AMD is working on a way to make a multi-core processor appear to
the host operating system as a single-core chip, it has been
claimed. If true, the move turns on its head the drive to develop
multi-threaded apps the better to take advantage of multiple
cores.
The technology is aimed at the next architecture after K8,
according to a purported company mole cited by French-language site
x86 Secret. It's well known that two CPUs - whether two
separate processors or two cores on the same die - don't generate,
clock for clock, double the performance of a single CPU. However,
by making the CPU once again appear as a single logical processor,
AMD is claimed to believe it may be able to double the single-chip
performance with a two-core chip or provide quadruple the
performance with a quad-core processor.
It's the very antithesis of the push for greater levels of
parallelism - performing more operations on data simultaneously, in
other words - in computer processors. Intel's HyperThreading, for
example, was developed to make use of under-utilised processor
components to fool the CPU into believing it had two processors at
its disposal, not one. Adding more cores just makes these virtual
cores real, and retaining the technology allows two cores to appear
as four.
Of course, better out-of-order execution techniques render
HyperThreading - Intel's version of the simultaneous
multi-threading (SMT) technique - less important. Put simply, they
ensure there are fewer parts of the pipeline going unused at any
given time, so there's less performance to be gained by throwing
extra threads at the processor. Indeed, Intel's briefings on its
next-generation architecture, due to debut in Q3 as the 'Conroe'
chip, play down HyperThreading and talk up out-of-order
execution.
But Conroe, so far as Intel is admitting, still appears as two CPUs
to the host OS. So is there anything to be gained by making it
appear as just one processor? Well, operating systems already do a
good job of scheduling hundreds of threads on a single-core CPU let
alone a dual- or quad-core part, and AMD may have found that OS is
so good at this that it can make up for the apparent reduction in
parallelism, particularly in cases where one thread predominates,
in a game, for instance.
However, by the time the technology ships - if it proves real, and
ever becomes more than a lab experiment - the software industry
will have had several years focusing on multi-threaded apps, and it
may not want to go back. ®