The Quest for Cores, the Thirst for Threads

[Dirk Broer]

Nowadays crunchers with deep pockets can use 18-core Xeon CPUs to fill their farms. Those 18-core Intel CPUs are by no means cheap!
They come in two variants, one for the 'old' Socket 2011 (DDR3 based) and one for the newer Socket 2011-3 (DDR4 based). When used in combination with the right Intel Xeon CPU (8000 series) and chipset, they can be stuck into Mobo's holding up to 8(!) of these behemoths. Your local hardware store will most likely not supply you with a board holding more than two of them, and most data centers will be satisfied with (mostly SuperMicro) boards holding four. Four times 18 cores is still 144 threads per board....

Over here I can buy four different 18-cores, what are the specs?

Model	Socket	Speed	Turbo*	TDP	Watt tdp/Core	Watt tdp/Thread
E7-8890 v3	2011	2.3 GHz	3.1 GHz	165 Watt	9.16	4.58
E7-8880 v3	2011	2.5 GHz	3.3 GHz	150 Watt	8.33	4.16
E7-8880L v3	2011	2.0 GHz	2.8 GHz	115 Watt	6.38	3.19
E5-2699 v3	2011-3	2.3 GHz	3.6 GHz	145 Watt	8.05	4.02

*=Max. single core performance.

And what has AMD to put against this? Till shortly, it had to do with 16-core Opterons, made out of 8 modules and not able to do more than 16 threads each.
This will change with the upcoming Zen CPU, that offers 32 cores and 64 threads (!) maximum per CPU. When AMD can keep the TDP below 150 Watt, it looks like a VERY attractive alternative to the Xeons. Intel doesn't sit still either and is busy with Xeons offering even more cores, 20 or even 22. But a quad Zen board would be able to do up to 256 threads, more than even the 22-core Xeon could do (at most 176 threads for a quad-cpu Xeon board with 22-core Xeons).

But to put the GHz, Watt/Core and Watt/Thread into perspective, let's look at Kabini:

Model	Socket	Speed	Turbo	TDP	Watt tdp/Core	Watt tdp/Thread
Athlon 5350	AM1	2.05 GHz	2.05 GHz	25 Watt	6.25	6.25
A4-5000	FT3	1.50 GHz	1.50 GHz	15 Watt	3.75	3.75

Not too bad! If you have nine of these Kabini's running -each with a 60 Watt laptop brick or Pico PSU- it compares nicely with one Xeon 18-core with a 540+ Watt PSU.
Both installations do 36 threads.
There are differences of course:

• Nine Kabini's will have a total of 18 MB L2 cache and no L3 cache, while the 18-core Xeons have 18x 256 KB= 4.5 MB L2 cache and 45 MB L3 cache.
• Kabini's will have to do with single-channel DDR3 RAM, while 18-core Xeons will use quad-channel DDR3 RAM (Socket 2011) or DDR4 RAM (Socket 2011-3).