2 ms·

Performance-intensive code (hot loops) could be compiled multiple times for each architecture extension and switched with CPUID. That's how all the various SSE

Performance-intensive code (hot loops) could be compiled multiple times for each architecture extension and switched with CPUID. That's how all the various SSE and AVX extensions were rolled out in multimedia code. AFAIK there was AVX512 in higher-end desktop SKUs, but not the latest E-core designs in Intel's client chips. The main problems are that: - Operations at 512-bit register widths have significant power draw. Intel chips that support AVX512 have to downclock themselves on AVX512 workloads until their voltage regulators have boosted up to a higher voltage. - The AVX512 register file is too big to physically fit in the E-core[0] footprint. Incidentally I do remember Linus Torvalds specifically complaining that AVX512 was being used to implement memcpy in gcc, because it meant running certain programs would lower system performance. So these new architectures tend to be used a lot sooner than the time it takes for it to be safe to make them your minimum compile target. [0] The BIOS on my Framework laptop refers to these as "Atom cores" - no clue if the current E-core design is derived from Atom or if this is a miscommunication or nickname AMI picked.

adrian_b 3y ago
No, operations at 512-bit register widths do not have significant power draw, as demonstrated by AMD Zen 4. What has significant power draw is the use of double 512-bit floating-point multipliers, as implemented in the Intel server CPUs (though one core with such multipliers draws significantly less power than two cores having the same throughput). AMD uses only double 256-bit floating-point multipliers and in general it uses exactly the same execution units for both 256-bit and 512-bit operations, so the AVX-512 operations do not increase the power draw even when they use 512-bit registers. Also the AVX512 register file is not too big to physically fit in the E-core. Even if the AVX512 register file is 4 times greater than the AVX register file, the E-cores have much a much larger register file used to rename the architecturally visible registers. Despite these facts, Intel still believes that implementing the full AVX-512 ISA in the E-cores is too expensive, so they have created this new specification of AVX10/256, which is just a subset of AVX-512 including the instructions with an operand size up to 256 bits, and which will be implemented in all future E-cores after some date, perhaps starting in 2025.
wmf 3y ago
Yes, E-cores are Atom cores. You can tell because they have -mont in the codename.
- adrian_b 3y ago
  Moreover, besides their history, the E-cores continue to be sold using the Atom brand, for instance "Intel Atom® x7425E" (the industrial variant of the Intel N100, one of the Alder Lake N models).

adrian_b 3y ago

No, operations at 512-bit register widths do not have significant power draw, as demonstrated by AMD Zen 4. What has significant power draw is the use of double 512-bit floating-point multipliers, as implemented in the Intel server CPUs (though one core with such multipliers draws significantly less power than two cores having the same throughput). AMD uses only double 256-bit floating-point multipliers and in general it uses exactly the same execution units for both 256-bit and 512-bit operations, so the AVX-512 operations do not increase the power draw even when they use 512-bit registers. Also the AVX512 register file is not too big to physically fit in the E-core. Even if the AVX512 register file is 4 times greater than the AVX register file, the E-cores have much a much larger register file used to rename the architecturally visible registers. Despite these facts, Intel still believes that implementing the full AVX-512 ISA in the E-cores is too expensive, so they have created this new specification of AVX10/256, which is just a subset of AVX-512 including the instructions with an operand size up to 256 bits, and which will be implemented in all future E-cores after some date, perhaps starting in 2025.

wmf 3y ago

Yes, E-cores are Atom cores. You can tell because they have -mont in the codename.

adrian_b 3y ago
Moreover, besides their history, the E-cores continue to be sold using the Atom brand, for instance "Intel Atom® x7425E" (the industrial variant of the Intel N100, one of the Alder Lake N models).