5 ms·

Sunny/Cypress Cove had lots of other area growth than just AVX-512 [1]. The better comparison is Skylake vs Skylake-SP, from which AVX512 is estimated to cost a

Sunny/Cypress Cove had lots of other area growth than just AVX-512 [1]. The better comparison is Skylake vs Skylake-SP, from which AVX512 is estimated to cost about 5% of the tile area [2]. So that’s the area cost of about 2 cores in the 28 core chip. [1] https://en.wikichip.org/wiki/intel/microarchitectures/sunny_cove#Key_changes_from_Palm_Cove.2FSkylake https://en.wikichip.org/wiki/intel/microarchitectures/sunny_... [2] https://www.realworldtech.com/forum/?threadid=193291&curpostid=193291 https://www.realworldtech.com/forum/?threadid=193291&curpost...

wtallis 5y ago
> The better comparison is Skylake vs Skylake-SP, from which AVX512 is estimated to cost about 5% of the tile area That analysis might be slightly underestimating the area penalty of AVX512, because the consumer Skylake cores that didn't have AVX512 execution units still reserved space for the AVX512 register file. (And given that fact, it's all the more surprising that while Intel was repeatedly refreshing 14nm Skylake for the consumer market, they never added the rest of the AVX512 bits or redid the layout of the consumer cores to reclaim the blank space of the register file.)
- brigade 5y ago
  Unlike the ALUs, it's trivial to locate and determine the area of a 512 bit x 168 register file. No way would Kanter have missed that in his analysis.
  - wtallis 5y ago
    It's not really a matter of whether Kanter missed those spots, but of whether subtracting them from the total core area is relevant to the question he was trying to answer. (Also, both the ALUs and the register files are trivial to locate by comparing die photos of consumer and server versions of the Skylake core.) If you're going to hypothesize about a rearranged Skylake core that no longer reserves space for the full 512 bit vectors in the register file, then you probably should also try to estimate the other area savings that would result from truly removing AVX512 from the core design at a high level, rather than merely masking off a few regions of silicon that serve no purpose other than AVX512 support. And answering that question is a lot more subjective than simply tallying up the area occupied by the extra execution units hanging off the side of the AVX512-enabled server Skylake cores. Or, to put it another way: there unquestionably is an area cost to AVX512 beyond that of the extra execution units tacked on to SKL-X cores. But that cost was already being paid by consumer CPUs years before SKL-X/SKL-SP shipped. So it wasn't really a contributing factor to the loss of two cores when Skylaked-derived Comet Lake was succeeded by Rocket Lake.

wtallis 5y ago

> The better comparison is Skylake vs Skylake-SP, from which AVX512 is estimated to cost about 5% of the tile area That analysis might be slightly underestimating the area penalty of AVX512, because the consumer Skylake cores that didn't have AVX512 execution units still reserved space for the AVX512 register file. (And given that fact, it's all the more surprising that while Intel was repeatedly refreshing 14nm Skylake for the consumer market, they never added the rest of the AVX512 bits or redid the layout of the consumer cores to reclaim the blank space of the register file.)

brigade 5y ago
Unlike the ALUs, it's trivial to locate and determine the area of a 512 bit x 168 register file. No way would Kanter have missed that in his analysis.
- wtallis 5y ago
  It's not really a matter of whether Kanter missed those spots, but of whether subtracting them from the total core area is relevant to the question he was trying to answer. (Also, both the ALUs and the register files are trivial to locate by comparing die photos of consumer and server versions of the Skylake core.) If you're going to hypothesize about a rearranged Skylake core that no longer reserves space for the full 512 bit vectors in the register file, then you probably should also try to estimate the other area savings that would result from truly removing AVX512 from the core design at a high level, rather than merely masking off a few regions of silicon that serve no purpose other than AVX512 support. And answering that question is a lot more subjective than simply tallying up the area occupied by the extra execution units hanging off the side of the AVX512-enabled server Skylake cores. Or, to put it another way: there unquestionably is an area cost to AVX512 beyond that of the extra execution units tacked on to SKL-X cores. But that cost was already being paid by consumer CPUs years before SKL-X/SKL-SP shipped. So it wasn't really a contributing factor to the loss of two cores when Skylaked-derived Comet Lake was succeeded by Rocket Lake.