[Beowulf] PCPro: AMD: what went wrong?

Vincent Diepeveen diep at xs4all.nl
Mon Feb 20 15:48:49 EST 2012


On Feb 20, 2012, at 9:29 PM, Lux, Jim (337C) wrote:

> Comments below about automated vs manual design..
>
>
> On 2/20/12 10:10 AM, "Mark Hahn" <hahn at mcmaster.ca> wrote:
>
>>> mid-range Core i5s. The verdict was unanimous; our sister title
>>> bit-tech dubbed the FX-8150 a ?stinker?.
>>
>> well, for desktops.  specFPrate scores are pretty competitive
>> (though sandybridge xeons are reportedly quite a bit better.)
>>
>>> Light was shed on Bulldozer?s problems when ex-AMD engineer Cliff
>>> Maier spoke out about manufacturing issues during the earliest  
>>> stages
>>> of design. ?Management decided there should be cross-engineering
>>> [between AMD and ATI], which meant we had to stop hand-crafting CPU
>>> designs,? he said.
>>
>> I'm purely armchair when it comes to low-level chip design, but to  
>> me,
>> this makes it sound like there are problems with their tools.  what's
>> the nature of the magic that slower/human design makes, as opposed to
>> the magic-less automatic design?
>
> One place where humans can do a better job is in the place and route,
> particularly if the design is tight on available space.  If there's  
> plenty
> of room, an autorouter can do pretty well, but if it's tight, you  
> get to
> high 90s % routed, and then it gets sticky.  It's a very, very complex
> problem because you have to not only find room for interconnects, but
> trade off propagation delay so that it can actually run at rated  
> speed:
> spreading out slows you down.  (same basic problem as routing printed
> circuit boards)
>
> Granted modern place and route is very sophisticated, but  
> ultimately, it's
> a heuristic process (Xilinx had simulated annealing back in the  
> 80s, for
> instance) which is trying to capture routine guidelines and rules (as
> opposed to trying guided random strategies like GA, etc.)

Actually for hand optimization of yields at modern CPU's stuff like  
simulated annealing is less popular.

You can actually also use lineair solvers for that, in order to  
recalculate entire design and under the right
constraints it gives an optimal solution, which is not garantueed for  
the non-lineair solving methods as
those also easily can pick a local maximum.

Stuff like simulated annealing is more popular at the non-lineair  
problems such as in artificial intelligence.


>
> Skilled humans can "learn" from previous similar experience, which  
> so far,
> the automated tools don't.  That is, a company doesn't do new CPU  
> designs
> every week, so there's not a huge experience base for a "learning"  
> router
> to learn from.
>
> The other thing that humans can do is have a better feel for  
> working the
> tolerances.. That is, they can make use of knowledge that some
> variabilities are correlated (e.g. Two parts side by side on the  
> die will
> "track", something that is poorly captured in a spec for the  
> individual
> parts).
>
> Pushing the timing margins is where it's all done.
>
>
>
>> is this a tooling-up issue that would
>> only affect the first rev of auto-designed CPUs?  does this also  
>> imply
>> that having humans tweak the design would make the GPU/APU chips  
>> faster,
>> smaller or more power-efficient?
>
>
> Historically, the output of the automated tools is very hard to  
> modify by
> a human, except in a peephole optimization sense.  This is because  
> a human
> generated design will typically have some sort of conceptual  
> architecture
> that all hangs together.  An automated design tends to be, well,
> unconstrained by the need for a consistent conceptual view.
>
> It's a lot harder to change something in one place and know that it  
> won't
> break something else, if you didn¹t follow and particpate the design
> process from the top.
>
> There's a very distinct parallel here to optimizing compilers and  
> "hand
> coded assembly".  There are equivalent tools to profilers and such,  
> but
> it's the whole thing about how a bad top level design can't be  
> saved by
> extreme low level optimization.
>
>
> Bear in mind that Verilog and VHDL are about like Assembler (even  
> if they
> have a "high level" sort of C-like look to them).  There are big
> subroutine libraries (aka IP cores), but it's nothing like, say, an
> automatically parallelizing FORTRAN compiler that makes effective  
> use of a
> vector unit.
>
>>
>> presumably this change from semi-manual to automatic design (layout?)
>> was motivated by a desire to improve time-to-market.  or perhaps  
>> improve
>> consistency/predictability of development?  have any such  
>> improvements
>> resulted?  from here, it looks like BD was a bit of a stinker and  
>> that
>> the market is to some extent waiting to see whether Piledriver is the
>> chip that BD should have been.  if PD had followed BD by a few  
>> months,
>> this discussion would have a different tone.
>
>
> There is a HUGE desire to do better automated design, for the same  
> reason
> we use high level languages to develop software: it greatly improves
> productivity (in terms of number of designs that can be produced by  
> one
> person).
>
> There aren't all that many people doing high complexity IC  
> development.
> Consider something like a IEEE-1394 (Firewire) core.  There are  
> probably
> only 4 or 5 people in the *world* who are competent to design it or at
> least lead a design: not only do you need to know all the  
> idiosyncracies
> of the process, but you also need to really understand IEEE-1394 in  
> all of
> it's funky protocol details.
>
> Ditto for processor cores.  For an example of a fairly simple and well
> documented core, take a look at the LEON implementations of the SPARC
> (which are available for free as GPLed VHDL).  That's still a pretty
> complex piece of logic, and not something you just leap into  
> modifying, or
> recreating.
> http://www.gaisler.com/cms/index.php? 
> option=com_content&task=view&id=156&It
> emid=104
>
>
>
>
>
>>
>> then again, GPUs were once claimed to have a rapid innovation cycle,
>> but afaikt that was a result of immaturity.  current GPU cycles are
>> pretty long, seemlingly as long as, say, Intel's tick-tock.  Fermi
>> has been out for a long while with no significant successor.  ATI
>> chips seem to rev a high-order digit about once a year, but I'm not
>> sure I'd really call 5xxx a whole different generation than 6xxx.
>> (actually, 4xxx (2008) was pretty similar as well...)
>
>
> I suspect that the "cycle rate" is driven by market forces. At some  
> point,
> there's less demand for higher performance, particularly for something
> consumer driven like GPUs.  At some point, you're rendering all the
> objects you need at resolutions higher than human visual  
> resolution, and
> you don't need to go faster.  Maybe the back-end physics engine  
> could be
> improved  (render individual sparks in a flame or droplets in a  
> cloud) but
> there's a sort of cost benefit analysis that goes into this.
>
> For consumer "single processor" kinds of applications we're  
> probably in
> that zone.. How much faster do you need to render that spreadsheet  
> or word
> document.  The bottleneck isn't the processor, it's the data pipe  
> coming
> in, whether streamed from a DVD or over the network connection.
>
>
>>
>>> Production switched to faster automated methods, but Maier says the
>>> change meant AMD?s chips lost ?performance and efficiency? as  
>>> crucial
>>> parts were designed by machines, rather than experienced engineers.
>>
>> were these experienced engineers sitting on their hands during  
>> this time?
>
>
> No, they were designing other things (or were hired away by someone  
> else).
>  There's always more design work to be done than people to do it.  
> Maybe
> AMD had some Human Resources/Talent Management/Human Capital issues  
> and
> their top talent bolted to somewhere else?  (there are people with  
> a LOT
> of cash in the financial industry and in government who are  
> interested in
> ASIC designs.. At least if the ads in the back of IEEE Spectrum and
> similar are any sign.)
>
> Being a skilled VLSI designer capable of leading a big CPU design  
> these
> days is probably a "guaranteed employment and name your salary"  
> kind of
> profession.
>
>
>>
>>> AMD?s latest chips haven?t stoked the fires of consumers, either.
>>> Martin Sawyer, technical director at Chillblast, reports that ? 
>>> demand
>>> for AMD has been quite slow?, and there?s no rush to buy Bulldozer.
>>
>> well, APU demand seems OK, though not very exciting because the CPU
>> cores in these chips are largely what AMD has been shipping for  
>> years.
>
>
> I would speculate that consumer performance demands have leveled  
> out, for
> the data bottleneck reasons discussed above.  Sure, I'd like to rip  
> DVDs
> to my server a bit faster, but I'm not going to go out and buy a new
> computer to do it (and of course, it's still limited by how fast I can
> read the DVD)
>>
>>> ?With no AMD solutions competitive with an Intel Core i5-2500K?, he
>>> says, ?AMD is a tough sell in the mid- and high-end market.? Another
>>> British PC supplier told us off-the-record that sales are partly
>>> propped up by die-hards who only buy AMD ?because they don?t like
>>> Intel?.
>>
>> to some extent.  certainly AMD has at various times in the past  
>> been able
>> to claim the crown in:
>> 	- 64b ISA and performance
>> 	- memory bandwidth and/or cpu:mem balance
>> 	- power efficiency
>> 	- integrated CPU-GPU price/performance.
>> 	- specrate-type throughput/price efficiency
>>
>> but Intel has executed remarkably well to take these away.  for  
>> instance,
>> although AMD's APUs are quite nice, Intel systems are power efficient
>> enough that you can build a system with an add-in-card and still  
>> match
>> or beat the APU power envelope.  Intel seems to extract more  
>> stream-type
>> memory bandwidth from the same dimms.  and Intel has what seems  
>> like a
>> pipeline already loaded with promising chips (SB Xeons, and  
>> presumably
>> ivybridge improvements after that).  MIC seems promising, but then  
>> again
>> with GCN, GPUs are becoming less of an obstacle course for  
>> masochists.
>
>
> Maybe Intel hired all of AMDs top folks away, and that's why AMD is  
> using
> more automated design? <grin>
>
>>
>> from the outside, we have very little visibility into what's going  
>> on with
>> AMD.  they seem to be making some changes, which is good, since  
>> there have
>> been serious problems.  whether they're the right changes, I  
>> donno.  it's
>> a little surprising to me how slowly they're moving, since being
>> near-death
>> would seem to encourage urgency.  in some sense, the current state  
>> is near
>> market equilibrium, though: Intel has the performance lead and is  
>> clearly
>> charging a premium, with AMD trailing but arguably offering decent  
>> value
>> with cheaper chips.  this doesn't seem like a way for AMD to grow  
>> market
>> share, though.
>
>
> But hasn't that really been the case since the very early days of  
> x86? I
> seem to recall some computers out in my garage with AMD 286 and 386  
> clones
> in them.
>
> AMD could also attack the embedded processor market with high  
> integration
> flavors of the processors.
>
>
> Does AMD really need to grow market share?  If the overall pie keeps
> getting bigger, they can grow, keeping constant percentage market  
> share.
> They've been around long enough that by no means could they be  
> considered
> a start=up in a rapid growth phase.
>
>
>>
>
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