Are 12 CPU Cores Faster Than 6 with Photoshop CS6?
With Photoshop CS5, testing showed that 6 cores were faster than 12 cores, a counter intuitive scenario for those who had invested in a “faster” Mac Pro.
With Photoshop CS6, improvements were made, in part based on feedback from Mac Performance Guide.
See also the extensive comparison review of Mac Pro models still 100% relevant on a comparative basis — done back in 2010.
Matching clock speed for apples-to-apples testing
Mac Pro 3.33 GHz 6-core: 24GB memory (8GB X 3), OWC Accelsior PCIe SSD
Mac Pro 3.33 GHz 12-core: 64GB memory (8/16/8GB X 2), OWC Accelsior PCIe SSD
The 12-core 3.33 GHz Mac Pro cannot be obtained from Apple; it was upgraded by OWC to dual 3.33 GHz 6-core CPUs. Apple’s fastest 12-core offering is 3.06 GHz.
Tests were repeated several times, results were highly consistent.
Testing on OS X 10.8.2 as of mid-November 2012 show that Photoshop CS6 retains internal multithreading inefficiencies that reduce its performance on a 12-core Mac Pro — even at identical clock speed to a 6-core model.
Apparently, Adobe still needs to work on multithreading code efficiency.
On the diglloydSpeed1 benchmark, the 3.33 GHz 6-core outperforms the 3.33 GHz 12-core by about 9%.
On the diglloydMedium benchmark, the 3.33 GHz 6-core outperforms the 3.33 GHz 12-core by about 22%.
Shown below is CPU usage during a 30 repetition run of diglloydSpeed1.
Observation of the HALF the available CPU power (even forgetting virtual CPU cores, which are pretty worthless).usage suggests ~300% CPU usage, or
There are six (6) real CPU cores and twelve virtual cores; 600% usage should be considered full CPU utilization— Photoshop is using half the available computing power.
Hence it should be no surprise that with multithreading coding inefficiencies and overhead, a 12-core CPU would run more slowly than a 6-core CPU.
12 cores is sometimes faster — of course!
A 6 core is definitely not faster than a 12-core for some tasks (namely certain video tasks and other tasks where more than six CPU cores are utilized), see the original review of the Mac Pro Westmere.
RAW file conversion is one such case. In general, 12-core vs 6-core is a choice to make based on actual workflow, and maximum memory requirements (e.g. 48GB max for 6 core vs 96GB max for 12 core).