The IBM POWER8 Review: Challenging the Intel Xeon
by Johan De Gelas on November 6, 2015 8:00 AM EST- Posted in
- IT Computing
- CPUs
- Enterprise
- Enterprise CPUs
- IBM
- POWER
- POWER8
Software Issues
So although the S824 is IBM's benchmark flagship for the scale-out range, the S812L and S822L are the servers that have the best chance at converting the kinds of users currently opt for x86 Xeons:
- Support for Little Endian data
- Best Linux support (Suse, Redhat & Ubuntu)
- (Somewhat) lower power
- 2U form factor which offers decent performance per U
- and probably the most important reason of all: Affordable! ($10k-25k instead of $30-60k)
So yes, the S822L looks like the first worthy alternative since 2010 for the dual Xeon servers. But the S822L did not inherit all the strong points of the typical "Big Blue" servers. The clockspeeds are a bit lower to keep the power consumption in check, and more importantly the LE Linux support is still very young. Sure, POWERLinux has been around for ages, but the software ecosystem was mostly supporting a few Big Endian applications like heavy duty Java servers and SAP.
Let's make the issue at hand a bit more tangible. IBM offers a migration advisor that helps developers to port their applications. That is definitely a good thing, but it also clearly illustrates that building a software ecosystem is a lot more cumbersome than the POWERPoint slides let you believe. In case of IBM's LE Linux, porting the rich x86 Linux software ecosystem to OpenPOWER is not that straightforward:
- Some code has inline x86 assembly such as thread resource locking code.
- Some code has x86 specific APIs
- No support for POWER in the make files which makes recompiling not straight forward
- POWER is 64 bit only.
We have experienced ourselves that this was more than just theory.
Case in point: for X86-64 we simply installed well tuned, ready to run, pre compiled binaries. Benchmarking is pretty easy here with a minor scripting effort.
The story was very different on the IBM S822L. We installed Ubuntu 15.04 (3.19.0-15 - ppc64le). To satisfy our curiosity we did a quick benchmark run with Linux-Bench, an automated benchmarking tool that Ian also likes to use. The benchmark did almost nothing on our POWER system despite the fact that most of the software had some form of support for POWER based systems.
The same was true for most software out there: We had to port most of the software by delving deep in all kinds of config, Readme, and make files. In many cases, we had to search around for alternative libraries that did support OpenPOWER.
Although a lot of software had an entry for "IBM POWER" in the make files, we encountered a lot of trouble. The server nor IBM is to blame: it is simply a fact that most developers - especially those with HPC software - have put a lot more effort in optimizing and validating their Intel x86 version of their software than the more "exotic" platforms.
Linux Ecosystem Not at Full Throttle.. Yet
It is clear to us that the OpenPOWER Linux ecosytem is still young and as a result does not offer the same performance as the older PowerVM and AIX platforms. There is still quite a bit of performance headroom.
A good example is the crypto acceleration. The IBM POWER8 has a dedicated cryptographic unit supporting new POWER ISA instructions to accelerate AES (Encryption), SHA (Hashing), and CRC (Cyclic Redundancy Check) codes. A similar encryption unit was already available in the POWER7+ . We found out that an nx-crypto driver was available and part of the Linux 3.5 kernel. However, even though Ubuntu 15.04 LE for OpenPOWER is based upon the Linux kernel 3.19, the nx-crypto driver was nowhere to be found. You could argue that the same is true for Intel as they introduce new instructions, but as far as we could see, there was no encryption acceleration whatsoever possible, not even based upon the older POWER7+.
A few days after we have finished testing, we found out the vmx-crypto driver will be available in distributions using the Kernel 4.1 and later and will be enabled in OpenSSL 1.0.2 (currently 1.0.1f in the standard repositories). The slide below - found in a presentation given this month - show how fast the ecosystem is expanding but also that it is still in flux.
OpenPOWER gained traction in 2014, the POWER8 is the first POWER chip with LE support and the number of Linux servers on top of OpenPOWER systems is still very small compared to x86. It is pretty simple: it is a much smaller community than the x86 linux server community. According to "the platform", IBM claims that "scale-out POWER8 machines have seen double digit revenue growth in the first half of 2015" but those growth numbers are "against a very small base". That tells us a lot: it is indeed a very small community, but a quickly growing one.
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Michael Bay - Saturday, November 7, 2015 - link
You are probably still hurry.Or just not civilized enough.
JohanAnandtech - Saturday, November 7, 2015 - link
I have to disagree with "only old legacy". One of things I really want to tackle is running Apache Spark on POWER. Spark is one of the most exciting Big Data tools, it is a very modern piece of software. IBM claims that the POWER8 is very good at it, and I want to check that.Jake Hamby - Friday, November 6, 2015 - link
Very interesting review! I've been a PowerPC fan for many years. I even bought a used PowerMac Quad G5 a few years ago to hack on FreeBSD for PowerPC with (much cheaper than the latest gear).My only suggestion is that I would love to see you run the same benchmarks with big-endian Linux, since the entire stack is so much more mature for PPC than LE Linux, which as you mention wasn't even supported for many years.
Anyone running Java workloads in particular has no business using LE Linux when Java itself uses big-endian data formats, and IBM has 15+ years of tuning the JDK for big-endian Linux & AIX.
TL;DR is the biggest advantage of LE Linux is that it's easier to port large custom apps that were written for x86 and have too many byte ordering issues to fix. The original motivation to make the PowerPC architecture bi-endian instead of big-endian was the hope of a Windows NT port. When Apple went their own way with hardware, and IBM focused on servers, little-endian mode disappeared. It's good that POWER8 supports LE mode again, for customers who really need it, but it's far from the normal mode.
PS. I've been working on fixing bugs in Clang/LLVM for PowerPC arch (32/64-bit). FreeBSD recently switched from GCC 4.2.1 (final GPLv2 version) to Clang as the default system compiler on x86, but LLVM has some code gen bugs for PowerPC that I'm hoping to squash. For now, it doesn't work well enough for me to recommend trying to use Clang as an alternative to GCC for POWER8 benchmarking. Certainly not for little-endian mode.
Jake Hamby - Friday, November 6, 2015 - link
BTW, the name of the instruction set architecture is still PowerPC, even though IBM's chips are the POWER series. The predecessor architecture was named POWER, so I always write PowerPC to avoid confusion when referring to the instruction set. The PowerPC 970MP chips in my Quad G5 (2 x dual-core) are a derivative of POWER4.ZeDestructor - Saturday, November 7, 2015 - link
That would be incorrect actually (since they changed since in 2006).The ISA is (currently) named the Power ISA (previously "PowerPC ISA", the "ISA" bit is quite important to denote hardware architecture vs ISA) (with the current being Power ISA 2.07 B)
Underneath each ISA, there are a variety of designs that all have nice, different names, from POWER1-8, PowerPC (including the various variants used by Apple, like the G5/970), Power-PC-AS, Cell, most LSI controllers (mostly PowerPC 440 (Power ISA 2.03) based, afaik) etc.
Source: https://en.wikipedia.org/wiki/Power_Architecture
tipoo - Friday, November 6, 2015 - link
I wish I had a what-if machine to see what IBM would be making had they stayed in the consumer space (well, discounting some consoles they're in - currently only the Wii U on an ancient PowerPC 750 modified for tri-core). And how chunky that PowerBook G5 would have been :Phttp://forums.macrumors.com/attachments/powerbook_...
DanNeely - Friday, November 6, 2015 - link
Probably they'd've ended up making architectural tradeoffs that made their cores a lot more like Intel. As it is, they can optimize their designs for very high power isn't a problem because the power cost is a small fraction of the TCO on one of their monster servers; and a relatively minor concern for consoles (ie just dropping the core count gets them desktop CPU level thermals which are good enough). If they were still selling to Apple, they'd need to be well optimized for performance at only a few watts/core for laptops. Huge L1 caches and massive SMT would be gone because they'd devour battery power to little benefit on systems that generally functioned at very low average CPU loads vs on a mega server or mainframe where if you're not pushing enough work onto it to keep it at a high load level you're doing it wrong.Jake Hamby - Friday, November 6, 2015 - link
Yep. It feels a lot like Apple's own 64-bit ARM cores have approached the old G5 (PPC 970) from the other end of the power envelope.Kevin G - Saturday, November 7, 2015 - link
While Apple's engineers were given the task of a PowerBook G5, they new it could never happen due to thermals and a very arcane chipset. Case in point, the PowerPC 970 could not boot itself: it needed a service processor to calibrate and initialize the frontside bus for the processor before it could take control. Justifiable for servers but unnecessary for a consumer laptop.The expected Powerbook G5's were supposed to be using PA-Semi chips. Due to IBM not meeting Apple's goals, they switched to Intel and the PA-Semi deal fell through with it. However, their dealings with Apple did lead to Apply buying them out a few years later to help design custom ARM SoCs and eventually the custom ARM cores used in the iPhone/iPad of today.
JohanAnandtech - Saturday, November 7, 2015 - link
Would love to hear some thoughts on what the possible problems could arise if we rerun our tests on BE linux. Because our best benchmarks are all all based upon some data stored on our x86 fileservers - so they are probably stored in LE.