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In part one of our investigation into Knights Landing, we described several possible options for the CPU core and came to the conclusion that Intel probably designed a custom core for Knights Landing. Over the past few weeks, a number of leaked presentations appeared online. Unsurprisingly, these leaks are equally illuminating and confusing. Most of the leaked slides are old and do not fully and accurately represent Intel’s choices for Knights Landing (KNL). That being said, the slides definitely contain helpful information – the trick is picking out the signal from the noise and extrapolating to other aspects of Knights Landing.
As a starting point, it is good to recap the information from the leaked slides:
- Products are targeting >3 TFLOP/s double precision
- Knights Landing uses 72 “Silvermont” cores
- Each “Silvermont” core includes 2 vector units
- Two “Silvermont” cores plus a shared 1MB L2 cache form a tile
- A mesh fabric routes between the tiles
- DDR4 memory controller
- Upto 16GB of on-package eDRAM
While some of these rumors are difficult to verify, quite a few check out. To start with, the rumored goal of >3 TFLOP/s double precision is quite sensible from a competitive and technology standpoint. KNL is built on a 14nm process and should deliver better than a 2× increase in performance over KNC – and 3 TFLOP/s is also consistent with the expected performance from Nvidia’s GPGPU focused offerings in a similar time frame.
Knights Landing is not fully compatible with the previous generation, since AVX-512 is encoded differently than LRBni – but it is likely that the two designs are highly ‘performance compatible’. More specifically, the architects for Knights Landing probably ensured that any software tuned for Knights Corner will run well on Knights Landing without additional effort. Understanding this guiding principle helps to validate many of these rumors and think about the overall architecture of Knights Landing.