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AMD cuts ‘Bulldozer’ instructions from ‘Zen’ processors

Advanced Micro Devices has been talking about development of its next-generation high-performance “Zen” architecture for months now, but so far it has not revealed any details about the chips officially. Nonetheless, thanks to a recent patch for Linux we have learnt one significant detail about “Zen”: it will not support many instructions found in the current-generation processors.

AMD recently started to enable support of its forthcoming “Zen” microprocessors in Linux operating systems. While typically patches to Linux distributives do not reveal a lot of micro-architectural peculiarities of various central processing units, this time is a clear exception. AMD explicitly revealed in the description of the patch to the GNU Binutils package that “Zen”, its third-generation x86-64 architecture in its first iteration (znver1 – Zen, version 1), will not support TBM, FMA4, XOP and LWP instructions developed specifically for the “Bulldozer” family of micro-architectures.

Elimination of such instructions clearly points to the fact that AMD’s new micro-architecture is a complete far cry from “Bulldozer”. The company even decided to remove support of the “Bulldozer”-specific instructions to save transistors and die space for something more useful. It seems that AMD now considers “Bulldozer” a dead-end and does not want to support even promising instructions introduced in the recent iterations of the company’s micro-architectures.

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While FMA4 and XOP could boost performance in gaming, HPC and multimedia applications, a promising thing that will be missed by numerous programmers is LWP, or lightweight profiling.

The lightweight profiling was developed to enable code to make dynamic and real-time decisions about how best to improve the performance of simultaneously running tasks, using techniques such as memory organization and code layout, with very little overhead. The LWP is a set of hardware features in AMD “Bulldozer” processors, which should be considered when designing applications.

AMD did not comment on the new-story.

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KitGuru Says: While it is sad to see many things go, it looks like “Zen” is so different from “Bulldozer” that it simply did not make sense to keep those instructions in the new processors. AMD probably believes that even without those instructions the new chips will be able to deliver competitive performance.

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