Mac Pro Speeds

(commentary)

There’s been a lot of speculation on what the Mac Pro CPUs might do to image processing speeds, but it’s been a little tough to interpret. Let’s see if I can clarify a bit. 

With modern Intel processors, they run at a clock speed, but they also have “turbo” abilities the increase the clock speed. Thus, when you just look at Mac Pro clock speeds, you see:

  • 4 core at 3.7Ghz  (0/0/0/2)
  • 6 core at 3.5Ghz  (1/1/2/2/2/4)
  • 8 core at 3.0Ghz  (4/4/4/4/5/7/8/9)
  • 12 core at 2.7Ghz  (3/3/3/3/3/3/3/4/5/6/7/8)


But these numbers can also be boosted (turbo) based upon the number of cores active. That’s what those numbers in parentheses are all about. Unfortunately, most people don’t understand how to read those parenthetical numbers. No worries, I’ll give the real scoop in a moment.

So, how many cores does your software actually use? For the most part, no more than four at the moment (includes Photoshop CS and CC). The maximum clock speeds with a turbo boost in place are for four core work are (all numbers in gigahertz):

  • 4 core Mac Pro 3.7Ghz — 3.9, 3.7, 3.7, 3.7
  • 6 core Mac Pro 3.5Ghz — 3.9, 3.7, 3.7, 3.7
  • 6 core Mac Pro 3.7Ghz — 4.0, 3.9, 3.8, 3.8
  • 15” Retina MacBook Pro 2.6Ghz — 3.8, 3.7, 3.6, 3.6
  • 27” iMac 3.5Ghz — 3.9, 3.9, 3.8, 3.7


From a pure CPU standpoint, none of the recent Macs are going to totally outperform another solely on CPU speed, as long as we assume that we’re only using a maximum of four cores for short periods of time.

However, there are other factors to consider:

  • GPU — Photoshop and other programs do take advantage of the video card GPUs these days, and the Mac Pro has dual GPUs and very state-of-the-art ones at that. I suspect much of the early benefits we'll see from Mac Pros on image processing are likely to come from that. 
  • Cache — Note the L3 Cache number for the various choices. In the Mac Pro models it ranges from 10MB on the lowest model to 30MB on the 12-core. More cache does have a benefit, though given the amount of data we’re moving through the CPU for image processing I would guess that it doesn’t make a huge difference. 
  • Thermal Design Power — The MacBook Pro can sustain up to 47 watts in a core, the iMac 84 watts, the Mac Pro 130 watts. This comes up when you’re doing sustained use of the turbo aspect of the CPU. The higher the wattage, the longer the CPU can run at turbo speed. If you’re doing processing for a single image, this probably isn’t a big factor. It certainly is a factor if you’re doing video transcoding of large clips for hours on end.


I’ve seen suggestions from others that the 6-core is the sweet spot in the Mac Pro lineup. Yes, if you’ve upgraded it to 3.7Ghz and upgraded the GPUs, I suspect that you’d see some performance boosts in Photoshop work, even before Adobe gets around to addressing the new capabilities. But I’m not sure those upgrades are worth the money at the moment. Of course, we all expect Adobe and everyone else creating software to try to figure out how to take advantage of “more,” so I wouldn’t be surprised if some day we see that Photoshop is actively managing a larger number of cores and GPUs to maximize performance on the Mac Pro and that makes a more discernible difference in your image processing. If you believe that to be the case, then you probably ought to look at the 6-core version, and you probably ought to look at the faster version of the 6-core machine, too, as it implies about a 5% speed boost over the base 6-core. 

To me, the Mac Pro isn’t so much a photography-oriented computer as it is a video-oriented one. Apple had a bit of a head start with Final Cut Pro, obviously, but what I see in one initial test with that program is that those extra cores and better GPUs do start to shine with network production-type work. Whereas I’ve been having to create proxy files—which takes considerable time, sometimes days, for the hours of video I’m feeding in—the Mac Pro has enough horsepower that it doesn’t need proxy files to run my editing needs. That’s a huge payoff in time, and it also reduces the storage requirements some, too.

We all want “more.” More pixels, more dynamic range, more processing speed, more memory, more drive size and performance. As always, however, it’s a matter of balance. For the time being, I’m sticking with my old Mac Pro for image processing, though I should note that it has been souped up with lots of memory and very fast SSD drives. I’m not really finding my current computer to be a bottleneck, even on D800 image processing. On the other hand, my current machine is a bottleneck on video, so I’m looking very closely at the new Mac Pro and evaluating my options.  

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