[Beowulf] Are mobile processors ready for HPC?

[Bogdan Costescu]

On Mon, May 27, 2013 at 5:28 PM, Eugen Leitl <eugen at leitl.org> wrote:

> The researchers point to the history of less expensive chips bumping out
> faster but higher-priced processors in high-performance systems. In 1993,
> the
> list of the world's fastest supercomputers, known as the Top500, was
> dominated by systems based on vector processors. They were nudged out by
> less
> expensive RISC processors like IBM's Power chip, whose use in
> supercomputers
> peaked early in the past decade. The RISC chips in turn were eventually
> replaced by cheaper commodity processors like Intel's Xeon and Advanced
> Micro
> Devices' Opteron, which today are used in more than 400 supercomputers on
> the
> Top500 list.
>

Please allow me to be skeptical.

The presentation again tells that the FP performance is at least one order
of magnitude lower for mobile processors than for desktop/server ones. I
found nice the comparison of bandwidth/FLOPs, which to me suggests that the
parallel scalability is comparable. Putting these two together means I get
my computational results with the same scalability but at least 10x slower.
To get the same performance, and assuming an ideal further scaling, I would
need at least 10x more processors, which will consume at least 10x more
power and cost at least 10x more. Hmmmm, I simply don't see the
advantage... same one ox versus 10 chicken we discussed many times. How
many ARM cores would one need to reach exaflops level ?

I also don't see how the history repeats in this case. Around year 2000,
desktop CPUs were at similar levels of performance with RISC ones, and at a
fraction of cost. But this doesn't hold for the current comparison.

One thing that I miss from the presentation is the power and cost of
interconnects. The current fast interconnects would allow a setup involving
many CPUs/nodes to scale further. But the current fast interconnects are
quite power hungry and expensive. Would anyone couple a 1W CPU with a 10W
NIC (ballpark figures) ? Or a 50EUR CPU with a 500EUR NIC (again, ballpark
figures) ? I wouldn't...

I can imagine mobile processors used in test clusters - good for teaching
about cluster architecture, development and especially scalability, with
low power and low cost. Embody the "cluster under my desk" concept. Also in
massive parallel file systems - like a HDD which doesn't have an onboard
SATA controller exposing a SATA interface to the outside, but a processor
talking directly to the drive electronics, exposing a Gigabit Ethernet (or
better...) interface and running your favorite parallel FS software. Or
similar for a RAM-based setup, where each memory module has one or more
processing cores attached to it. For such applications, the reasonable
memory access speed coupled with the low cost and low power requirements of
mobile processors are indeed an advantage. As long as there is not much FP
involved...

Cheers,
Bogdan



On Mon, May 27, 2013 at 5:28 PM, Eugen Leitl <eugen at leitl.org> wrote:

>
>
> http://www.pcworld.com/article/2039798/smartphone-chips-could-replace-server-processors-in-hpc-researchers-say.html
>
> Smartphone chips may power servers, researchers say
>
> Agam Shah, IDG News Service
>
> @agamsh May 25, 2013 12:50 PMprint
>
> Looking at historical trends and performance benchmarks, a team of
> researchers in Spain have concluded that smartphone chips could one day
> replace the more expensive and power-hungry x86 processors used in most of
> the world's top supercomputers.
>
> "History may be about to repeat itself," researchers at the Barcelona
> Supercomputing Center wrote in a paper titled "Are mobile processors ready
> for HPC?" The paper was presented at the EDAworkshop13 in Dresden, Germany,
> this month.
>
> Chip Wars
>
> The researchers point to the history of less expensive chips bumping out
> faster but higher-priced processors in high-performance systems. In 1993,
> the
> list of the world's fastest supercomputers, known as the Top500, was
> dominated by systems based on vector processors. They were nudged out by
> less
> expensive RISC processors like IBM's Power chip, whose use in
> supercomputers
> peaked early in the past decade. The RISC chips in turn were eventually
> replaced by cheaper commodity processors like Intel's Xeon and Advanced
> Micro
> Devices' Opteron, which today are used in more than 400 supercomputers on
> the
> Top500 list.
>
> The transitions had a common thread, the researchers wrote: Microprocessors
> killed the vector supercomputers because they were "significantly cheaper
> and
> greener," they said.
>
> "Mobile processors are not faster ... but they are significantly cheaper,"
> the researchers wrote.
>
> ]SNIP]
>
>
> http://www.montblanc-project.eu/sites/default/files/publications/Are%20mobile%20processors%20ready%20for%20HPC.pdf
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