Mac Pro 2013. 8-core vs 6-core. Looking for advice.

[Introvert]

Hi all

I'm going to buy a Mac Pro. Fully loaded. I'm just getting stuck at the CPU options.

I do music production as well as 3D rendering along with a little BootCamp gaming including the Dolphin (Wii) emulator.

I'm trying to decided between the 8-core and 6-core model. While multiple cores are important for 3D and music work, I'm also interested in good old-fashioned clock speed for single/dual core apps like Dolphin and PC gaming.

The 6-core runs at 3.5GHz with a turbo boost to 3.9GHz. The 8-core runs at 3.0GHz but also has a turbo boost to 3.9GHz.

As far as I can tell, there's very little difference between the 3.0GHz and 3.5GHz processors. Sure, the marketing says it's 500MHz but looking at the turbo boost and core scaling information, it looks as if they're almost identical for single core applications because of the 3.9GHz turbo boost on both CPUs.

More information here:
http://www.marco.org/2013/11/26/new-mac-pro-cpus

Can anyone shed some more light on the differences between the 6 and 8 core processors?

Thanks!

 

[sirio76]

The 8core have slightly better single core performance and about 25% faster multithreaded performance(for stuff like rendering). Decide by yourself if this is enough to justify the price premium over the 6core. IMO complete a render in 60' instead of 45' probably is not going to change your life
That being said I've opted for the 8core version.

 

[Sko]

25% faster multithreaded performance

Hmm, isn't that more about 15%? Because if all cores are working, there isn't any turbo. So it's (6*3.5) : (8*3) = 21:24 = 0.875 ≈ 12.5% (or 24:21 = 1.143 ≈ 14% from the other side).

So w
[W]ithin a given budget, I'd make sure to max out GPU and SSD (and RAM, but that's 3rd party of course) and go to 8 core only if there is some money left.

If your workflow contains heavy rendering where 60 mins vs. 53 [45] mins is mission critical, you probably should invest the 1.5 grand in a Linux based render slave.

 

[h9826790]

Hmm, isn't that more about 15%? Because if all cores are working, there isn't any turbo. So it's (6*3.5) : (8*3) = 21:24 = 0.875 ≈ 12.5% (or 24:21 = 1.143 ≈ 14% from the other side).

The E5-1680 v2 has Turbo Boost 2.0, that means turbo is avail with all core active. The turbo step of E5-1680 v2 is (4/4/4/4/5/7/8/9). So, if condition permit, all core can run at 3.4GHz, and may momentarily excess the TDP limit.

So, 8x3.4=27.2, and 6x3.6=21.6

(27.2 - 21.6)/21.6 ≈ 26%

 

[sirio76]

Hmm, isn't that more about 15%? .

No, all the 8core are effectively running @3.4ghz under full load(read the stepping information about this, also linked by the op). In practice if you run a well threated application like Cinebench15 you will get 25% or more performance from the 8core(there is plenty of test about this, just browse on Barefeats ecc).
Agree about an additional renderslave(if the renderer support DR). With little more than 1000$ you can build a 6core I7 machine that will easily double the render performance of a 6core nMP.

 

[Sko]

So, 8x3.4=27.2, and 6x3.6=21.6
(27.2 - 21.6)/21.6 ≈ 26%

Oh, I see. Thanks for clarifying.

 

[Radiating]

So to be clear the. 8 core is better in all single core applications.

 

[Introvert]

Thanks for the replies. I'm still a little confused.

Let me use an example. Imagine I'm running an app that's only optimized for two cores and it's utilizing two cores to the max.

Would the 3.0GHz 8-core turbo boost two of its cores to 3.9GHz and let the other 6 cores idle?

And how would this compare to the 3.5GHz 6-core. Would it also crank two of its cores to 3.9GHz and let the other 4 cores idle.

In this scenario would the 6-core and 8-core effectively produce the same turbo boosted 3.9GHz performance?

And yes, I plan to select 64GB ram and the D700s. Money is no object in this instance. I'm just trying to work out if I should get the 6 core or 8 core to get the best single/dual core performance in older apps where increased frequencies win over number of cores.

Thanks!

 

[h9826790]

Let me use an example. Imagine I'm running an app that's only optimized for two cores and it's utilizing two cores to the max.

In your example, ideally...

The 6-core will let 2 cores run at 3.7GHz but leave the rest at idle.

The 8-core will let 2 cores run at 3.8GHz and leave the rest at idle.

 

[Introvert]

In your example, ideally...

The 6-core will let 2 cores run at 3.7GHz but leave the rest at idle.

The 8-core will let 2 cores run at 3.8GHz and leave the rest at idle.

Cool. So to clarify:

The 8 core - even though it's a 3.0GHz processor - will outperform the 6-core 3.5GHz processor when using one or two cores only.

So, if an app can only use 1 or 2 cores - the 3.0GHz 8-core processor will out perform the 6-core in a 1 or 2 core utilization scenario?

And so, if you can afford it, the 8-core is the best configuration to get for that balance of single core app performance and multi core performance (when needed)?

Am I on the right track here?

 

[theSeb]

In your example, ideally...

The 6-core will let 2 cores run at 3.7GHz but leave the rest at idle.

The 8-core will let 2 cores run at 3.8GHz and leave the rest at idle.

Except that this won't happen because it's not only the "app that uses 2 cores" that will be running.

 

[Sko]

So, if an app can only use 1 or 2 cores - the 3.0GHz 8-core processor will out perform the 6-core in a 1 or 2 core utilization scenario?

As I read it, the 8-core will out perform the 6-core in every scenario as it has a doubled L3 cache to compensate for the minor Ghz disadvantage when using 4, 5 or 6 cores.

 

[pertusis1]

Geekbench single core speeds:

8-core - 3548
6-core - 3592

I would say the single core speed difference is negligible.

8-core - 25520
6-core - 20713

Any multi-threaded application will be 'significantly' faster on the 8-core. Depending on your work flow, this may be unimportant, or it might be huge. If it saves you 10 seconds 30 times daily, that's a big deal in my book... but then one of my least favorite things in life is waiting on computers :roll eyes:

By the way, have you considered buying the 4-core and upgrading to the 10-core. A lot of people think this may be the sweet spot for performance. Look up the 'Amazing 10 core Late 2013 Mac Pro Upgrade' thread.

 

[Introvert]

Thanks all. An 8-core it is.

 

[scottrichardson]

I strongly recommend reading this article from Anandtech, it explains in great detail the breakdown of the CPU's and the way their turbos work - illustrating just what clock speed you get when using different numbers of cores at once.

http://www.anandtech.com/show/7603/mac-pro-review-late-2013/4

See the graph here:

You can see the green line is the 6 core model where it is faster than the 8-core model when using 4, 5 or 6 of its cores. The 8-core was faster when using 2 cores, and equal speed at single and triple-core usage. I would hazard a guess and say if 100Mhz makes a big difference to you, and your general daily use is basic stuff, then the 8 core is probably better, but as soon as you start pulling 4 cores or more, then the 6-core has a slight advantage. Obviously if you need more than 6 cores, then you have no choice but to go 8 or 12 cores.

An alternative would be to buy the base quad core model then purchase an aftermarket 8-core XEON from Newegg that has a higher clock speed than the ones Apple offers.

 

[sirio76]

as soon as you start pulling 4 cores or more, then the 6-core has a slight advantage.

If a program can use more than 4core is very likely that it will use of all the present core and the 6core will be soon outperformed by the 8core. Since the op need this machine for 3d render and money is not an issue the 8core represent the best single/multicore combo.