ARM Challenging Intel in the Server Market: An Overview
by Johan De Gelas on December 16, 2014 10:00 AM ESTRISC vs. CISC Revisited
The RISC vs. CISC discussion is never ending. It started as soon as the first RISC CPUs entered the market in the mid eighties. Just six years ago, Anand reported that AMD's CTO, Fred Weber was claiming:
Fred said that the overhead of maintaining x86 compatibility was negligible, at the time around 10% of the die was the x86 decoder and that percentage would only shrink over time.
Just like Intel today, AMD claimed that the overhead of the complex x86 ISA was dwindling fast as the transistor budget grew exponentially with Moore's law. But the thing to remember is that high ranking managers will always make statements that fit their current strategy and vision. Most of the time there is some truth in it, but the subtleties and nuances of the story are the first victims in press releases and statements.
Now in 2014, it is good to put an end to all this discussion: the ISA is not a game changer, but it matters! AMD is now in a very good position to judge as it will develop x86 and ARM CPUs by the same team, lead by the same CPU architecture veteran. We listened carefully to what Jim Keller, the head of the AMD CPU architect team, had to say in the 4th minute of this YouTube video:
"The big fundamental thing is that ARMv8 ISA has more registers (32), a three operand ISA, and spends less transistors on decoding and dealing with the complexities of x86. That allows us to spend more transistors on performance... ARM gives us some inherent architectural efficiency."
You can debate until you drop, but there is no denying that the x86 ISA requires more pipeline stages and thus transistors to decode than any decent RISC ISA. As x86 instructions are variable length, fetching instructions is less efficient and requires more transistors. The instruction cache is also larger as you need to store pre-decode information. The back-end might deal with RISC-like micro-ops but as the end result must adhere to rules of the x86 ISA, thus transistors are spent on exception handling and condition codes.
It's true that the percentage of transistors spent on decoding has dwindled over the years. But the number of cores has increased significantly. As a result, the x86 tax is not imaginary.
Hardware Accelerators
While we feel that the ARMv8 ISA is definitely a competitive advantage for the ARM server SoCs, the hardware accelerators are a big mystery: we have no idea how large the performance or power advantage is in real software. It might be spectacular or it might be just another "offload works only in the rare case where all these conditions are met". Nevertheless, it is interesting to see how the ARM server SoC has many different integrated accelerators.
Most of them are the usual IPSec, TCP offloading engines, and Cryptographic accelerators. It will be interesting to see if the ARM ecosystem can offer more specialized devices that can really outperform the typical Intel offerings.
One IP block that got my attention was the the Regex accelerators of Cavium. Regular expression accelerators are specialized in pattern recognition and can be very useful for search engines, network security, and data analytics. That seems exactly what we need in the current killer apps. But the devil is in the details: it will need software support, and preferably on a wide scale.
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jhh - Tuesday, December 16, 2014 - link
SPARC and Power have had trouble keeping up with Moore's law, as neither sold enough to amortize R&D to push out innovation at the same rate as Intel. As Moore's law comes to an end, this will stop being a unique Intel advantage. It just might be too late for both of them. One can see the pressure on IBM, with their opening the Power architecture in similar ways to ARM. Both POWER and SPARC have to keep up to porting drivers to their Unix implementations, while the device manufacturers either write drivers for Linux or don't get volume. I just can't see either POWER or SPARC being cost effective over the long run. And, when others see the same thing, they aren't going to be excited about porting application software to those platforms.ARM needs to have a good performance/power and performance/cost ratio to get people excited to buy something other than Intel. They are certainly getting enough volume from the low-end to make investment on high-end parts. So far, I'm not excited enough to recommend any ARM proof-of-concept though.
Kevin G - Wednesday, December 17, 2014 - link
IBM always had a licensing model similar to ARM with PowerPC cores. The only thing really new here is that IBM is licensing out there flagship POWER chip in the same manner. Despite Intel having a process advantage, IBM was able to keep up in performance. (The 45 mm based 8POWER7 was generally faster than the 32 mm 10 core Westmere-EX.) There will always be a market for top performance but you are correct that sustaining on just that customer base is unwise.IBM does realize that their software licensing model to subsidize hardware R&D was not sustainable. So while you can't run AIX, you can get a POWER8 box for less than $3k now.
OreoCookie - Wednesday, December 17, 2014 - link
Really, just $3000? Wow, how times have changed, I remember ~12 years ago that a single Alpha CPU cost that much (the department I was working for had a workstation fail, fortunately under warranty, because otherwise they would have had to pay for 2 new CPUs and new RAM worth about 15,000 German Marks).Ratman6161 - Wednesday, December 17, 2014 - link
"The general lower cost of Linux and open source software" While it's true that the cost of a Linux OS including support is lower than an equivalent Windows OS, in the larger scheme of things the cost of Windows and even VMware becomes little more than background noise in the total cost of operations. Try pricing out an Oracle DB for example and you find that the cost of that software dwarfs the price of the hardware it's running on as well as whatever the OS is costing. Ditto with most "enterprise software".lefty2 - Tuesday, December 16, 2014 - link
Intel has another big advantage over ARM, which everyone seems to have forgotten about, and that is software compatibilty. 64-bit ARM server software is still a work in progress. The stuff that's being worked on at the moment is open source. Once that's finished you still have to convince clients to convert their proprietary software to ARM.JohanAnandtech - Tuesday, December 16, 2014 - link
Don't you think that the open source software that has been/is ported now is enough? Apache/PHP/MySQL, Memcached and Hadoop...that is a massive server market. And there is little stopping Microsoft to invest in ARM software too. Just VMware might be a bit tricky, but I don't think the software is a problem.Kevin G - Wednesday, December 17, 2014 - link
Actually VMware has said some less that flattering about ARM. Xen is the main hyper visor on ARM for the moment.goop666666 - Thursday, December 25, 2014 - link
Yeah, recompiling is so very hard. Essentially what you're saying is that Intel is for legacy systems and software that is poorly written. That is a large enough market, but doesn't apply to hyperscale deployments, which are the future.gostan - Tuesday, December 16, 2014 - link
great article by Johan as always.but the argument is muted. we have heard this tune before.
the hardware might be cheaper. the power bill might be cheaper. wait until you see the software maintenance cost. custom software needs 'custom' pricing.
besides, arm has no cutting edge fab process to back them.
JohanAnandtech - Tuesday, December 16, 2014 - link
You do not need expensive software to create a server market these days. Just look how many webservers are running the LAMP stack.