Assessing IBM's POWER8, Part 2: Server Applications on OpenPOWER
by Johan De Gelas on September 15, 2016 8:01 AM ESTEnergy Consumption
A large part of the server market is very sensitive to performance-per-watt. That includes the cloud vendors/hosts. For a smaller part of the market, top performance is more important than the performance/watt ratio. Indeed, for financial trading, big data analyses, large databases, and most HPC servers, total performance is the top priority. Energy consumption should not be outrageous, but it is not the most important concern.
We tested the energy consumption of our servers for a one-minute period in several situations. The first one is the point where the tested server performs best in MySQL: the highest throughput just before the response time goes up significantly. Then we look at the point where throughput is the highest (no matter what response time). This is the situation where the CPU is fully loaded.
| SKU | TDP (on paper) spec |
Idle Server W |
MySQL Best Throughput at Lowest Resp. Time (W) |
MySQL Max Throughput (W) |
Transaction /s |
Tr/watt |
| IBM POWER8 S812LC | 190 W | 221 | 259 | 260 | 14482 | 55 |
| Xeon E5-2699 v4 | 145 W | 67 | 213 | 235 | 18997 | 89 |
| Xeon E5-2690 v3 | 135 W | 84 | 249 | 254 | 11741 | 47 |
Throughput and single threaded performance were the priorities for designing POWER8. Power consumption stood probably much lower on the list, way behind RAS. The idle power shows us that you should not use the POWER8 in applications that run at low load for long periods.
Intel's "Broadwell-EP" (Xeon E5 v4), by comparison, is the clear victor when it comes to performance per watt, and even without looking at Intel's background, it's clear from the data alone that more thought was put into that aspect.
However, considering that the POWER8 was launched around the same time as Intel Haswell, IBM's multicore delivers a lot of integer performance per watt of energy it consumes. In fact, despite the power gobbling Centaur chips, despite the fact that MySQL is not the most POWER8 optimized application, IBM's medium range POWER8 is capable of defeating Intel's Haswell. While this is less relevant to the server buyer today, it does show that IBM's engineering capabilities are competitive with Intel, which is good news for the upcoming POWER9 chip. The POWER9 chip will be the first POWER chip which has specific SKUs for the affordable scale out servers.
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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