[Beowulf] Is there really a need for Exascale?

Mark Hahn hahn at mcmaster.ca
Wed Nov 28 22:14:39 PST 2012


>> Commodity mother boards are similar or equal to supercomputer
>> hardware.

uh, sorta.
first, ECC.  when I'm feeling particularly surly, I'd claim that ECC
is not commodity - it's smaller volume, higher price, almost unheard
of in the high-volume (consumer) market.  (which is appropriate, 
since it's hard to justify ECC for a mostly idle desktop that 
occassionally wakes up to fetch a page you clicked on ;)

but yeah, whitebox server stuff is fairly commoditized, and is or 
is similar to what comprises a lot of top500 machines.  but there 
are also BG machines in there, or the K machine, or ...
those are not commodity parts, and have a somewhat different set of 
design tradeoffs.  IBM certainly thinks much harder about scalability
(fabric design, MTBF of very large clusters, etc) than Supermicro does,
or even HP/Dell.

let me put it this way: when you buy a server from HP or Dell, you're 
getting a box optimized to maximize their business: give the customer
warm fuzzies, minimize returns and service under warranty, etc.
until recently, it would have integrated scsi, for instance, which 
tends not to be relevant to HPC.  heck, integrated video is not even 
strictly HPC-relevant.

>>  But I wonder what will drive further improvements in
>> reducing power usage by several orders of magnitude.

several orders of magnitude?  I'm not sure why this is even believed
to be possible.  servers have improved from, say, >300W a few years 
ago to more like 250 today.  power-performance has improved a lot more,
of course, but that's certainly not due to anything done at the MB level.

>> I've heard
>> the suggestion that computers in cell phones will be the mass
>> market that leads to low-power hardware suitable for supercomputers.

doh.  sorta.  obviously mobile cares about power because of batteries.
it's less clear that "wired" computers will ever care that much - 
how much will people notice their desktop taking 20 rather than 30W?

>> But the cell phone components do not cover the same range as
>> supercomputer components.
>
> But is that really true.   Sure, the processor in a cellphone is slower
> than say a typical modern PC CPU.. But, given appropriate software, is it
> a better $/FLOPS or W/FLOPS deal to get 100 cellphone CPUs or 1 superduper
> PC CPU?

again, every one knows you get better performance/power if you go low.
but too-slow processors are a problem to connect efficiently.

>> What do others in the mailing list see as the trend?  Does the
>> development of mass-market consumer products suffice for meeting
>> the needs of the HPC community during this decade and the next?

consumers don't buy IB, and it's the standard HPC interconnect.  beowulf
has always been about repurposing commoditized parts where possible,
but not exclusively.

> At some point, light speed becomes the limiting factor, and for that,
> reducing physical size is important.

we're quite a way away from that.  I don't see a lot of pressure to 
improve fabrics below 1 us latency (or so), ie, 1000 light-feet.

> Consumer gear is heading smaller, in
> general (viz PC mobos getting smaller over the years),

mainly due to integration, not anything else.  intel put cache onchip
because it made performance sense, not because it freed up a few 
sq inches of motherboard.

> production density.  Consumer markets have the advantage of enormous
> volumes to spread the very high non-recurring-engineering cost over.

actually, the remarkable thing is that it seems to cost a lot less 
to produce custom parts these days.  if you (like facebook or google)
want a custom motherboard, I bet there are 20 companies that will 
design and produce it for you for much less cost than 10 years ago...

> delays).  How much is that worth?  10 million? 100 million?  (engineering
> a new cellphone probably costs in the area of 10M, for context..  The

I'm not so sure about that.  take the recent nexus4 phone: it's pretty
much the same range of off-the-shelf components as Apple or Samsung use.
the trick, as with any consumer product, is to find the right design
to stimulate the purchase reflex.  for a long time, only Apple seemed 
to know how to do this consistently.


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