Assessing IBM's POWER8, Part 2: Server Applications on OpenPOWER
by Johan De Gelas on September 15, 2016 8:01 AM ESTRecent Developments: OpenPOWER's Potential HPC Comeback
Those who suggested that IBM's scale out servers were just a half-hearted effort that would quickly get strangled by the desire to protect the high margin big iron servers could not have been more wrong. IBM just launched 3 new servers, and all of them are affordable scale out servers. IBM is now very aggressively going after the market it has (almost) completely lost to Intel's Xeon: HPC. At the same time IBM is emphasizing the determination to play an important role in the emerging "machine learning" and "Big Data" market.
The S822LC "Big Data" and S821LC use mature and proven – some would say "older" – technology: the "OpenPOWER version" of the POWER8 and NVIDIA's Tesla K80. There are some interesting new facts to discuss though. First of all, these servers are made by Supermicro, confirming the close relation between the two companies and that OpenPOWER is indeed "Open". Supermicro is the market leader in the HPC market, and the fact that Supermicro chose to invest in OpenPOWER is a promissing sign: IBM is on to something, it is not another "me too" effort.
Secondly, these servers use (registered) DDR4 RAM as opposed to DDR3 as found in servers like the S812LC and SL822. Since they are still communicating via the "Centaur" memory buffers, this will not give any tangible performance boost, but it means that the servers are making use of the most popular and thus cheapest server memory technology.
The 2U S822LC "Big Data" looks like a solid offering. Pricing starts at $5999 (one 3.3 GHz 8-core, 64 GB RAM, no GPU), but realistically a full equipped server (two 10-cores, one K80, 128 GB) is around $16000. If you do not need the GPU, a server with two 10-cores, 256 GB, 2x 10 GB and two 1 TB disks costs around $13341. The CPU inside is still the 190W TDP single chip 10-core (at 2.9-3.5 GHz boost) that we tested a while ago. There is also an 8-core (3.3 - 3.7 GHz boost) alternative.
The 1U S821LC starts at $5900. The 1U form factor limits the POWER8 to much lower power envelopes. The 8-core chip runs at 2.3 GHz (135W TDP), the 10-core is allowed to consume a greater 145W, but runs at a meager – for POWER8 standards – 2.1 GHz. We can imagine that this is indeed based upon the customer feedback of space constrained datacenters, as IBM claims. We feel however that it makes the S821LC server less attractive as one of the distinguishing features of the POWER8 is the high single threaded performance. The POWER8 was simply not designed to run inside a 1U server. On the other side of the coin, a 2.1 GHz 10-core might still be fast enough to feed the GPU with the necessary data in some HPC applications.
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nils_ - Monday, September 26, 2016 - link
Isn't the limit slighty lower than 32 GiB? At some point the JVM switches to 64 bit pointers, which means you'll lose a lot of the available heap to larger pointers. I think you might want to lower your settings. I'm curious, what kind of GC times are you seeing with your heap size? I don't currently have access to Java running on non virtualised hardware so I would like to know if the overhead is significant (mostly running Elasticsearch here).CajunArson - Thursday, September 15, 2016 - link
All in all the Power chip isn't terrible but the power consumption coupled with the sheer amount of tuning that is required just to get it competitive with the Xeons isn't too encouraging. You could spend far less time tuning the Xeons and still have higher performance or go ahead with tuning to get even more performance out of those Xeons.On top of the fact that this isn't a supposedly "high end" model, the higher end power parts cost more and will burn through even more power, and that's an expense that needs to be considered for the types of real-world applications that use these servers.
dgingeri - Thursday, September 15, 2016 - link
That ad on the last page that claims lower equipment cost of course compares that to an HP DL380, the most overpriced Xeon E5 system out right now. (I know because I shopped them.) Comparing it to a comparable Dell R730 would show less expense, better support, and better expansion options.Morawka - Thursday, September 15, 2016 - link
you mean a company made a slide that uses the most extreme edge cases to make their product look good?!?! Shocking /sGondalf - Thursday, September 15, 2016 - link
Something is wrong is these power consumption data. The plataform idles at 221W and under full load only 260W?? the cpu is vanished?? Power 8 at over 3Ghz has an active power of only 40W??1) the idle value is wrong or 2) the under load value is wrong. All this is not consistent with IBM TDP official values.
IMO the energy consumption page of the article has to be rewrite.
JohanAnandtech - Thursday, September 15, 2016 - link
We have double checked those numbers. It is probably an indication that many of the power saving features do not work well under Linux right now.BTW, just to give you an idea: running c-ray (floating point) caused the consumption to go to 361W.
Kevin G - Thursday, September 15, 2016 - link
I presume that c-ray uses the 256 bit vector unit on POWER8?Also have you done any energy consumption testing that takes advantage of the hardware decimal unit?
mapesdhs - Thursday, September 15, 2016 - link
C-ray isn't that smart. :D It's a very simple code, brute force basically, and the smaller dataset can easily fit in a modern cache (actually the middling size test probably does too on CPUs like these). Hmm, I suppose it's possible one could optimise the compilation a bit to help, but I doubt anything except a full rewrite could make decent use of any vector tech, and I don't want to allow changes to the code, that would make comparisons to all other test results null. Compiler optimisations are ok, but not multi-pass optimisations that feed back info about the target data into the initial compile, that's cheating IMO (some people have done this to obtain what look like really silly run times, but I don't include them on my main C-ray page).Ian.
Gondalf - Tuesday, September 20, 2016 - link
Ummm so in short words the utilized sw don't stress at all the cpu, not even the hot caches near the memory banks. We need a bench with an high memory utilization and a balanced mix between integer and FP, more in line with real world utilizationI don't know if this test is enough to say POWER8 is power/perf competitive with haswell in 22nm.
In fact POWER market share is definitively at the historic minimum and 14nm Broadwell is pretty young, so this disaster it is not its fault.
jesperfrimann - Wednesday, September 21, 2016 - link
If you have a OPAL (Bare Metal system that cannot run POWERVM) then all the powersavings features are off by default AFAIR.Try to have a look at:
https://public.dhe.ibm.com/common/ssi/ecm/po/en/po...
Many of the features does have a performance impact, ranging from negative over neutral to positive for a single one.
But Again. I think your comparison with 'vanilla' software stacks are relevant. This is what people would see out of the box with an existing software stack.
It is 101% relevant to do that comparison as this is the marked that IBM is trying to break into with these servers.
But what could be fun to see was some tests where all the Bells and Whistles were utilized. As many have written here.. use of Hardware supported Decimal Floating Point. The Vector Execution unit, the ability to do hardware assisted Memory Compression etc. etc.
// Jesper