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Core i7-4770K: Haswell's Performance, Previewed

Results: Sandra 2013

Although Dhrystone isn’t necessarily applicable to real-world performance, a lack of software already-optimized for AVX2 means we need to go to SiSoftware’s diagnostic for an idea of how Haswell’s support for the instruction set might affect general integer performance in properly-optimized software.

The Whetstone module employs SSE3, so Haswell’s improvements over Ivy Bridge are far more incremental. 

Sandra’s Multimedia benchmark generates an image of the Mandelbrot Set fractal using 255 iterations for each pixel, representing vectorised code that runs as close to perfectly parallel as possible.

The integer test employs the AVX2 instruction set on Intel’s Haswell-based Core i7-4770K, while the Ivy and Sandy Bridge-based processors are limited to AVX support. As you see in the red bar, the task is finished much faster on Haswell. It’s close, but not quite 2x.

Floating-point performance also enjoys a significant speed-up from Intel’s first implementation of FMA3 (AMD’s Bulldozer design supports FMA4, while Piledriver supports both the three- and four-operand versions). The Ivy and Sandy Bridge-based processors utilize AVX-optimized code paths, falling quite a bit behind at the same clock rate.

Why do doubles seem to speed up so much more than floats on Haswell? The code path for FMA3 is actually latency-bound. If we were to turn off FMA3 support altogether in Sandra’s options and used AVX, the scaling proves similar.

All three of these chips feature AES-NI support, and we know from past reviews that because Sandra runs entirely in hardware, our platforms are processing instructions as fast as they’re sent from memory. The Core i7-4770K’s slight disadvantage in our AES256 test is indicative of slightly less throughput—something I’m comfortable chalking up to the early status of our test system.

Meanwhile, SHA2-256 performance is all about each core’s compute performance. So, the IPC improvements that go into Haswell help propel it ahead of Ivy Bridge, which is in turn faster than Sandy Bridge.

The memory bandwidth module confirms our findings in the Cryptography benchmark. All three platforms are running 1,600 MT/s data rates; the Haswell-based machine just looks like it needs a little tuning.

We already know that Intel optimized Haswell’s memory hierarchy for performance, based on information discussed at last year’s IDF. As expected, Sandra’s cache bandwidth test shows an almost-doubling of performance from the 32 KB L1 data cache.

Gains from the L2 cache are actually a lot lower than we’d expect though; we thought that number would be close to 2x as well, given 64 bytes/cycle throughput (theoretically, the L2 should be capable of more than 900 GB/s). The L3 cache actually drops back a bit, which could be related to its separate clock domain.

It still isn’t clear whether something’s up with our engineering sample CPU, or if there’s still work to be done on the testing side. Either way, this is a pre-production chip, so we aren’t jumping to any conclusions.

Chris Angelini is an Editor Emeritus at Tom's Hardware US. He edits hardware reviews and covers high-profile CPU and GPU launches.