You could use SOI, no bulk.

I don't get the point of the AC. Light bulbs and space heaters are AC
powered and still disipate power. What did I miss?

On Oct 24, 9:40 pm, Andrew Reilly <andrew-newsp... at (no spam) areilly.bpc-



users.org> wrote:
On Sat, 24 Oct 2009 12:25:40 -0700, Robert Myers wrote:
I don't have any insight into what being architecture-naive on the other
architectures might be, but, for Itanium, you have to start with deep
insight into the code in order to get a payback on all the fancy bells
and whistles.  Itanium should be getting more instructions per clock,
not significantly fewer (that *was* the idea, wasn't it?).

I've not used an Itanium, but it would seem to have quite a bit of
practical similarity to the Texas Instruments TIC6000 series of VLIW DSP
processors, in that it is essentially in-order VLIW with predicated
instructions and some instruction encoding funkiness.  That whole idea is
*predicated* on being able to software-pipeline loop bodies and do enough
iterations to make them a worthwhile fraction of your execution time.  
From memory, Anton's TeX benchmark is the exact opposite: strictly
integer code of the twistiest non-loopy conditional nature.  I would not
expect even a heroic compiler to get *any* significant parallel issues
going, at which point it falls back to being an in-order RISC-like
machine: not dramatically unlike a pre-Cortex ARM, or SPARC, as you said.

Now, Texas' compilers for the C6000 *are* heroic, and I've seen them
regularly schedule all eight possible instruction slots active per cycle,
for appropriate DSP code.  The interesting thing is that this process is
*extremely* fragile.  If the loop body contains too many instructions
(for whatever reason), or some other limitation, then the compiler seems
to throw up its hands and give you essentially single-instruction-per-
cycle code, which is (comparatively) hopeless.  Smells like a box full of
heuristics, rather than reliable proof.  The only way to proceed is to
hack the source code into little pieces and try variations until the
compiler behaves "well" again.

At least the TI parts *do* get low power consumption out of the deal, and
since they clock more slowly they don't have quite so many cycles to wait
for a cache miss.  And no-one is trying to run TeX on them...

I get so tense here, trying to make sure I don't make a grotesque
mistake.

Your post made me chuckle.  Thanks.  I actually didn't even look at
the TeX numbers, only the ones I had first relied upon.  As a seventh-
grade teacher remarked, my laziness might one day be my undoing.

Thanks for calling attention to the TI compiler.  I've looked at the
TI DSP chips, but never gotten further.

You know just how heroic a heroic compiler really is.  I don't know
whether David Dinucci (did I get it right?) is still following.

I don't have any insight into what being architecture-naive on the other
architectures might be, but, for Itanium, you have to start with deep
insight into the code in order to get a payback on all the fancy bells
and whistles. Itanium should be getting more instructions per clock,
not significantly fewer (that *was* the idea, wasn't it?).

In article <4AE12FA9.1000706 at (no spam) patten-glew.net>,
Andy \"Krazy\" Glew <ag-news at (no spam) patten-glew.net> wrote:
Robert Myers wrote:

I am not aware of an Itanium shipped or proposed that had an "x86 core
on the side".

I am. I can't say how far the proposal got - it may never have got
beyond the back of the envelope stage, and then got flattened as a
project by management.

Robert Myers wrote:
Let's see.  Quantum mechanics properly applied takes account of
everything in the whole universe, which is, so far as I know, quantum
mechanical and reversible in it's entirety.

Nope.  That's just wishful thinking from people who do QM.  The concepts
behind decoherence are partly understood, and some even quantified (e.g.
the critical temperature corresponds to what has been called "thermal
de-Broglie wavelength", which more or less describes the relation
between random changes in the conductor and a "volume of coherence"),
but overall, this is not part of QM.  QM describes what happens within
the volume of coherence, classical physic describes what happens
outside.  There is no accepted unified theory that gives a good reason
for this boundary and works equally well on both sides of the coherence
fence.

Note that when the "observer" is actually a quantum mechanical object,
it won't disturb the other parts of the system - it will be part of this
reversible dance.

Thus, even though you can't do operations with *no* net cost in
energy, we can still build and operate devices that act as quantum
mechanical computers to an arbitrarily good approximation.

No, we can't.  The quantum computer people are struggling with the same
thermal de-Broglie wavelength as the superconducting people.  Just that
in quantum computing, the wavelength also depends on how many bits your
system has - but unfortunately, it goes exponentially with the number of
bits.  So you can either make it arbitrary slow for many bits, or reduce
the number of bits to an almost useless amount, but not both at the same
time.

When I say something like "you can build and operate" I am not meaning

An in-order cpu requires the asm programmer and/or compiler writer to
figure out statically how long each of those chains will be, and then
unroll the code sufficiently to handle it. This btw. requires a _lot_
more architectural registers, and is quite brittle when faced with a new
cpu generation with slightly different latency numbers.

Over the years I have learned that, if at a dead end, one must ask
stupid questions and come up with blue sky ideas, questioning the
implicit assumptions of the field, and/or starting from first
principles.   Apparently we are approaching such a dead end wrt
circuits.  I'm not *that* afraid to embarrass myself.  My definition of
a computer architect is the guy who is able to go in and call "Bullshit"
on any specialist in the team who is sandbagging and/or reporting
obstacles.  I've simplified logic by 100x.  Dave Papworth, my former
boss on P6, once showed that the process technology guys were
sandbagging by more than 30% - he asked me for my CRC Handbook of
Chemistry and Physics, looked up the physical properties of aluminum,
and went and banged heads together.

I can't help but wonder if this is part of the problem: the search for
the perfect, the lowest possible power, as opposed to what can be done now.

Your theories of how binary translation works is interesting, because
Gforth 0.7.0 works like such a naive binary tranlator for
straight-line Forth code: It just concatenates the code fragments for
the VM instructions in the Forth code sequence together.  However, for
VM control flow, Gforth uses indirect branches, and even naive binary
translators are more sophisticated.  I also doubt that the
PA-RISC->IA64 binary translator is as naive as Gforth for
straight-line code.

I don't have enough insight into the other architectures to comment.
I first looked at the chart and said, yup, just like I said, it's a
compiler built and tuned around x86.

I just happened to have your charts fresh in mind when I made the
comment, and neither your results nor the fact that binary translation
doesn't work well is a surprise.

Robert Myers wrote:
Coherence theory is a *huge* improvement over talking about things
like "the collapse of the wavefunction," but I don't find the idea of
drawing a box and saying things are quantum mechanical within it and
"classical" outside it to be particularly helpful.

It obviously is a very simplified view.  Yes, there is no obvious and
"hard" boundary e.g. between coherent and incoherent light.  It's just
to illustrate: the "classical physics" which we are used to, as it
describes human-scale effects, deals with incoherent light and matter.  
QM deals with coherent light and matter.  It's not so easy to say "just
put incoherent light into QM equations, and off you go with your
classical physics".  QM tends to turn incoherent parts into coherent,
even when applied to larger scales (from Bose-Einstein condensate to
lasers), classical physic does the reverse.

On Oct 25, 4:10 am, Terje Mathisen<terje.wiig.mathi... at (no spam) gmail.com
I don't mind Kudos from you Robert, but I don't think I deserve it
this time:

I didn't post anything about Linus' OoO ideas.

Terje, you were kind enough to explain to me, in a private
correspondence, that, no matter how inept the coder or the compiler,
OoO hardware would eventually figure out and exploit a circumstance
where software pipelinging might conceivably have been helpful. That
is to say (not your words, but mine) OoO hardware knows how to do
software pipelining, even if, in some rare awkward instances, it might
take a while.

Och! Wounded I am, ad-hominem'ed. What did I ever do to you, Bernd?
Have you been taking lessons from Nick?

However, what I am talking about - what I have picked up from
researchers in this field - is to still have power and ground rails at
(1.5V,0) - but to have signal rails that are at (+1.3,+0.7). Then
signal rails periodically reverse, to (+0.7,+1.3).
This is why, in my original post, I was careful to say `The
devices
will have to work within a range of changing voltages, say when "high"
is between k=1/3 and k=1 Vmax=(Vmean+k*Vswing), and "low" is between
k=1/3 and k=1 Vmin=(Vmean-k*Vswing).'
Where signal rails at (+0.7,+1.3) range, with power rails at
(+1.5,0), Vmean=1V, VSwing = 0.3V, Vmax=1.3V, Vmin=0.7V.

Can this be made to work? I'm sure that Bernd will tell me an answer;
and, if I am lucky, we may get an answer frm somebody with more
knowledge than either I or Bernd have. I think you can keep the
devices properly biased under such a scheme.
But then again, this is not my specialty.

Even if it can be made to work, is there any advantage to doing it?

(It's interesting to think about why AC ultimately beat the DC systems
that Edison initially deployed. I don't think power efficiency in the
device was a big part; mainly it was the ability to transmit AC longer
distances, with the ease of transformers to change voltage level.
Dissipation in transmission was part of it. I don;t know if this has
any relevance to electronics.)

Over the years I have learned that, if at a dead end, one must ask
stupid questions and come up with blue sky ideas, questioning the
implicit assumptions of the field, and/or starting from first
principles. Apparently we are approaching such a dead end wrt
circuits. I'm not *that* afraid to embarrass myself. My definition
of a computer architect is the guy who is able to go in and call
"Bullshit" on any specialist in the team who is sandbagging and/or
reporting obstacles.

I can't help but wonder if this is part of the problem: the search for
the perfect, the lowest possible power, as opposed to what can be done
now.

Anyway, this may be a moot point. IEEE Spectrum October 2000, p.40
has an article by Pushkar Apte & George Scalise at the SIA, mentioning
graphene base BiSFET (Bilayer pseudo-Spin Field Effect Transistors)
(not
to be confused with BISFET, the BI-Stable FET). They say the BiSFET
"needs only one-hundredth to one-thousandth the power of a standard
MOSFET".

Coherence theory is a *huge* improvement over talking about things
like "the collapse of the wavefunction," but I don't find the idea of
drawing a box and saying things are quantum mechanical within it and
"classical" outside it to be particularly helpful.

Del Cecchi wrote:
You could use SOI, no bulk. :-)

There still is a bulk, there is just no substrate, so the bulk is
left
floating. The diodes I mentioned are sill there, supplying the bulk
when forward biased (this is the well-known effect of SOI to have
variable gate thresholds through charging and discharging the bulk
below
the diodes threshold, unless you add in a real bulk contact like on
stock silicon wafers).

I don't get the point of the AC. Light bulbs and space heaters are
AC
powered and still disipate power. What did I miss?

I can't tell you. Andy apparently doesn't care much about the
physics
behind integrated circuits, his knowledge stops at the gate level.
This
is completely ok for digital design, but I wonder why he makes that
sort
of suggestions .

One interesting property of quantum mechanics is that for
irreversible
logic, there's a minimum amount of energy that is necessary to make
it
happen. Reversible logic does not have this drawback. Therefore,
people investigate into reversible logic, even though the actual
components to get that benefit are not in sigh (not even carbon
nanotube
switches have these properties, even though they are much closer to
the
physical limits for irreversible logic). Many people also forget
that
quantum mechanics does not properly take changes in the system into
account, and that means that your reversible logic only works with
the
predicted low power when the inputs are not changing any more - and
this
is just the uninteresting case (the coherent one - changes in the
system
lead to decoherence, and thereby to classical physics).

--
Bernd Paysan
"If you want it done right, you have to do it yourself"
http://www.jwdt.com/~paysan/

I don't know actually know of any circumstances, though, where any run-
time software approach yields significant benefits, other than for
languages like Java that *can't* run without run-time support. If I
knew of such an instance, that would be a good place to start thinking
about a theory of binary translators, but I don't know of any such
instances.