Design Con 2015
Breaking News
Comments
Newest First | Oldest First | Threaded View
Page 1 / 3   >   >>
servernut
User Rank
Rookie
CPU freq does not mean performance
servernut   6/6/2014 2:30:27 PM
NO RATINGS
I was amused to see the Cavium CEO quote GHz/socket and use that to claim performance superiority over Intel. Does he really think the analysts and reporters would be fooled by that?

 

Oh wait, I just remembered this article and Linley's quotes. I guess he succeeded. What does that say about the competence of these so called analysts?

 

TarraTarra!
User Rank
CEO
Re: 48 core power would be very high
TarraTarra!   6/5/2014 11:17:14 AM
NO RATINGS
@Wilco1, @GSMD,

The debate on ISAs is interesting. I have designed x86 CPUs and other ISAs as well. It is a fact that x86 is inherently more complex than MIPS or ARM or PowerPC to varying degrees. There is certainly the CISC instruction decode penalty but there are other complex mechanisms that have been built into x86 over generations which still need to be supported by the latest x86 processors. All of these mechanisms take die-size and/or complexity. Almost every implementation of x86 CPU has a built in micro-code engine. This is like a programable engine within the CPU to handle these complex tasks. Intel has continued to stress floating point performance and each generation adds additional instructions adding transistors to the design.

So why is this relevant? This "overhead" becomes smaller in very high performance implementations - out-of-order, multi-threaded, large cache designs. Here the overhead can be amortized over the performance gains of a complex CPU. This is why Intel has competed well at the very high end compute but failed in low power efficient designs that are required for mobile.

In these less complex implementations where the CPU has fewer transistors, this overhead starts to make a difference. This is why the mobile processors from Intel and even the Atom cores have not competed so well.

 

Wilco1
User Rank
CEO
Re: 48 core power would be very high
Wilco1   6/5/2014 8:25:39 AM
NO RATINGS
Well it's obvious you've never looked in detail at the complexity of the x86 ISA. The overheads of x86 affect the whole microarchitecture. With an identical microarchitecture x86 would end up slower (and thus less power efficient). For x86 to achieve the same performance as a RISC, it needs a far more complex microarchitecture, increasing die size and power. You can compare die sizes for various ARM and x86 CPUs here: http://chip-architect.com/news/2013_core_sizes_768.jpg

The claim that x86 has a dense encoding is yet another myth. In fact the complex encoding means that x86 binaries are typically a little larger than ARM binaries, and significantly larger than Thumb-2. x64 is usually 15% larger than x86.

Yes I've read that paper and discussed it in detail on RWT. It is a badly written paper with most of the conclusions not supported by evidence. If you choose to compare wildly different and relatively ancient CPUs, an old compiler and completely ignore the memory system then of course the only possible conclusion is that microarchitecture matters the most! But that's only true if you make wild extrapolations and ignore or handwave at all other aspects. Let's hope this paper was a one-off mistake and doesn't reflect on the quality of papers coming from this university.

Note PPC is certainly not CISC. Neither is ARM or Thumb. PPC vs ARM is less interesting as their ISA features are nearly identical (not that there aren't differences but the differences tend to be insignificant details).

Wilco1
User Rank
CEO
Re: 48 core power would be very high
Wilco1   6/4/2014 3:51:15 PM
NO RATINGS
GSMD, a few comments on your points:

1. It's a myth that ISA overhead is just in decode. There are many aspects of an ISA that affect the overall microarchitecture. Just to mention one example, x86 requires more load/store units due to having fewer registers and load+op instructions. x86 also uses a more complex memory ordering model.

2. Given they designed their own CPU it seems likely Cavium are aiming for better than Cortex-A57 performance, as otherwise they could have just licensed that (the same argument applies to X-Gene). A 3-way in-order is not completely implausible, but to get decent throughput it would need to be at least 2-way and ideally 4-way multithreaded.

4. If all else is equal, an identically performing x86 would use more power than ARM due to its more complex ISA. So the x86 ISA really is LESS efficient. Of course different processes, microarchitectures etc can mitigate this difference.

In any case there is no doubt a dedicated CPU can outperform a generic Xeon despite having a process disadvantage (as you say in point 5). Beating Xeon on single-threaded performance is much harder of course, but that is not something Cavium or X-Gene are attempting (at least with their current line-up). For many tasks, using more, slower cores is actually far more energy efficient.

 

rick merritt
User Rank
Author
Re: 48 core power would be very high
rick merritt   6/4/2014 6:19:42 AM
NO RATINGS
@GSMD: Good points! I'd love to hear results from your lab tests when they are done.

rick merritt
User Rank
Author
Re: 48 core power would be very high
rick merritt   6/4/2014 6:14:34 AM
NO RATINGS
@Servernut: Applied definitely got out there early. I have written 3-4 stories about them so far. I am not a Computex so would love to hear the latest. For a while they have been in Cavium's spot: we have been waiting for them to ship and report performance specs. Anyone have an update on that?

servernut
User Rank
Rookie
Re: Software for ARM servers
servernut   6/4/2014 2:33:31 AM
NO RATINGS
"Now I'd like to hear some reality about where we are at and need to be at in server software for ARM"

 

Rick, 

Here is some information on XGene's recent demo with the software stack. 

http://www.informationweek.com/cloud/infrastructure-as-a-service/energy-sipping-arm-chips-made-for-cloud/d/d-id/1269308

 

servernut
User Rank
Rookie
Re: 48 core power would be very high
servernut   6/4/2014 2:23:07 AM
NO RATINGS
@Rick. Cavium's Octeon designs are not out-of-order but in-order. Thunder is likely to be the same. All other server CPUs - Xeons, Opterons, even X-Gene are fully out-of-order machines.

 

Actually XGene from appliedmicro is completely missing from your post. They showed a mini-datacenter running at Computex this week. Any reason, you are not covering them? They seem to be shipping already. From the specs they seem to have everything that thunder is claiming and a few years ahead.

What are your thoughts on XGene?

rick merritt
User Rank
Author
Re: 48 core power would be very high
rick merritt   6/4/2014 12:40:16 AM
NO RATINGS
@Servernut and/or Hank: Can one of you briefly explian what the Octeon OOO-like scheme is and how it is different in performance to full OOO?

Perhpas B'com's promise of a full OOO quad issue FinFET-based processor will be significantrly more powerful...AMD';s planned K-12, too. But those are likely 2016 chips.

rick merritt
User Rank
Author
Software for ARM servers
rick merritt   6/4/2014 12:29:23 AM
NO RATINGS
Thx all for your good points on the chips.

Now I'd like to hear some reality about where we are at and need to be at in server software for ARM if this borader initiative of which Cavium is just one part is going to get traction. Details, please!

Page 1 / 3   >   >>


Most Recent Comments
sempaiscuba
 
sempaiscuba
 
sempaiscuba
 
chipchap42
 
sempaiscuba
 
sempaiscuba
 
David Ashton
 
Duane Benson
 
sixscrews
Top Comments of the Week
Flash Poll
Like Us on Facebook

Datasheets.com Parts Search

185 million searchable parts
(please enter a part number or hit search to begin)
EE Life
Frankenstein's Fix, Teardowns, Sideshows, Design Contests, Reader Content & More
Max Maxfield

Max's BADASS Display: A Comedy of Errors
Max Maxfield
4 comments
Good grief -- where does the time go? I first determined to build my Bodacious Acoustic Diagnostic Astoundingly Superior Spectromatic (BADASS) display way back in the mists of time we used ...

<b><a href=Betajet">

The Circle – The Future's Imperfect in the Present Tense
Betajet
5 comments
The Circle, a satirical, dystopian novel published in 2013 by San Francisco-based writer Dave Eggers, is about a large, very powerful technology company that combines aspects of Google, ...

Martin Rowe

Make This Engineering Museum a Reality
Martin Rowe
Post a comment
Vincent Valentine is a man on a mission. He wants to make the first house to ever have a telephone into a telephone museum. Without help, it may not happen.

Rich Quinnell

Making the Grade in Industrial Design
Rich Quinnell
16 comments
As every developer knows, there are the paper specifications for a product design, and then there are the real requirements. The paper specs are dry, bland, and rigidly numeric, making ...

Special Video Section
The LT8640 is a 42V, 5A synchronous step-down regulator ...
The LTC2000 high-speed DAC has low noise and excellent ...
How do you protect the load and ensure output continues to ...
General-purpose DACs have applications in instrumentation, ...
Linear Technology demonstrates its latest measurement ...
10:29
Demos from Maxim Integrated at Electronica 2014 show ...
Bosch CEO Stefan Finkbeiner shows off latest combo and ...
STMicroelectronics demoed this simple gesture control ...
Keysight shows you what signals lurk in real-time at 510MHz ...
TE Connectivity's clear-plastic, full-size model car shows ...
Why culture makes Linear Tech a winner.
Recently formed Architects of Modern Power consortium ...
Specially modified Corvette C7 Stingray responds to ex Indy ...
Avago’s ACPL-K30T is the first solid-state driver qualified ...
NXP launches its line of multi-gate, multifunction, ...
Doug Bailey, VP of marketing at Power Integrations, gives a ...
See how to ease software bring-up with DesignWare IP ...
DesignWare IP Prototyping Kits enable fast software ...
This video explores the LT3086, a new member of our LDO+ ...
In today’s modern electronic systems, the need for power ...