A Tale of 3 Processors

As is always the case, everytime you try to compare implementations, you find completely unexpected bugs. The idea was simple: look at the performance of the last few generations and see how we’ve been improving.

To start with, I have a Core2 Quad, Q8400 at 2.66GHz (fixed frequency) and a venerable 3rd generation Intel GPU (a q35 to be precise). This is a 95W desktop beast, only to be beaten by a slightly older Q9550 Core2 Quad at 2.83GHz sporting a 4th generation GPU, a g45.

From the current generation of CPU design, I have two mobile chips, a Sandybridge i5-2520m at up to 3.2GHz and an Ivybridge i7-3720qm at up to 3.6GHz. These mobile chips run much cooler than their desktop brethen at 35W and 45W respectively, and both have the GT2 variants of the 6th and 7th generation Intel GPUs.

To put those two into perspective, I have also added the results from a desktop Sandybridge chip, the 95W i5-2500 which runs up to 3.7GHz. On the downside this processor only has a GT1 6th generation GPU.

Compared to the baseline performance given by the Core2 Q8440:

Q9550: 1.6x faster
i5-2500: 2.3x faster
i5-2520m: 1.7x faster
i7-3720qm: 1.4x faster

The success story is that the 35W mobile processors really do deliver the performance of the 95W desktop beasts of the previous generation, which is quite frankly very impressive. Of course, they are still dwarfed by their desktop brethen – now I really do want to get my hands on a i7-3770k!

The oddity is then why is my Ivybridge underperforming? Its single thread performance which is under test here should not be as badly limited, the base clock is a tiny bit faster than the Sandybridge i5, and with the larger and improved caches it should acheive better IPC as well. In theory it should also be coupled to faster main memory as well. My guess is that it is being throttled due to poor cooling. Or that there is a glitch in the software, or perhaps a broken configuration, or perhaps the memory is underrated, et cetera.

But what of the graphics performance, I hear you cry! The situation here is a bit more complex. All of those processors where using the same SSE2 backend in pixman which will only be improved upon with the introduction of AVX2 in Haswell, and so we were directly comparing slight variations of processor design executing the same software. When we look at GPU performance, not only do we have a wide variation of processor design, feature set and instruction sets, we also by necessity have different software for each.

If we look at the current driver situation, that is using UXA:

Compared to the baseline performance given by using SNA on the Core2 Q8440 with a q35 (a gen3 device like found in the Pineview netbook) GPU:

Q9550: 4.3x slower
i5-2500: 1.5x slower
i5-2520m: 3.0x slower
i7-3720qm: 2.3x slower

Despite almost a doubling of CPU power and an even greater increase in the GPU performance across the generations, the drivers continue to do a disservice to the hardware and ourselves.

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