4 ms·

It isn’t “sour grapes”, I remember when the HPC community largely abandoned these benchmarks two decades ago because they weren’t representative of anything rea

It isn’t “sour grapes”, I remember when the HPC community largely abandoned these benchmarks two decades ago because they weren’t representative of anything real for most of them. The benchmark is a poor reflection of real workloads. There was a long period when the STREAM benchmark was the primary correlate with real-world performance for most HPC workloads but you can’t build a press release from that. I don’t have a dog in this fight and I no longer work in HPC. Most modern workloads are severely bandwidth bound. The only aspect of the hardware that matters is bandwidth and that is not materially differentiated. The frontier is scheduler design, which is pure software and difficult computer science. HPC competitions avoid problems with a software solution because it isn’t in their interest as hardware manufacturers. This result is impressive, sort of, but not in the way people are imagining. I was equally dismissive of the previous leader for the same reasons. For most applications, these benchmarks are legacy pagentry.

adrian_b 4mo ago
As I have mentioned, and as described in TFA, this supercomputer is also leading in memory bandwidth (4 TB/s per socket => correction, it is 8 Tb/s per socket). I agree with what you say about benchmarks, but that is precisely why the advantage of this supercomputer over the following American supercomputers will be even greater in more demanding workloads than Linpack and HPCG. It has already shown this by having an advantage in HPCG of greater than 26% over the fastest US system, while in Linpack its advantage is of only 22%. Thus its position in the top cannot be dismissed as insignificant, because it more likely underestimates than overestimates this system. Also the programming effort for writing an efficient program will be lower than for the GPU-based US supercomputers.
- jandrewrogers 4mo ago
  I definitely appreciate the CPU-centric approach. It appeals to my biases and aligns with my technical perspective. The memory bandwidth is something you can buy. Exotics were >1 TB/s over a decade ago, so 4 TB/s in 2026 is not that impressive. For all practical purposes, these CPUs are also still exotics, you can’t just buy them. I would be very surprised if the memory bandwidth of US exotics haven’t improved over the last 10-15 years. In any case, for real workloads scalability is mostly a software theory problem at this point and that is still a dark art without much literature.
  - adrian_b 4mo ago
    Correction, I took the 4 TB/s from TFA, but the NextPlatform article clarifies that it is 4 TB/s per chiplet, but 8 TB/s per socket, so more impressive. The only US-designed CPU "exotics" are the Intel Xeon Max CPU series, which use HBM like the Chinese CPUs, but which have a theoretical maximum throughput of only 1.6 TB/s per socket, i.e. 5 times slower than the new Chinese CPUs. Moreover, the users of Intel Xeon Max complained that they cannot reach the theoretical memory bandwidth. I do not know if that was due to some bug that might have been solved later by Intel with a microcode update or a new mask set stepping. The server CPUs with standard DIMMs, which will be launched by AMD and Intel next year, will have a memory bandwidth of around 1 TB/s per socket. The AMD MI300 GPU used in the fastest US supercomputer has a memory throughput of 5.2 TB/s per socket, so lower than the 8 TB/s per socket of the Chinese CPU, which explains why the advantage of the Chinese system increases in the benchmarks more dependent on memory performance. The latest AMD Instinct GPU, MI355X, increases the memory bandwidth to 8 TB/s, so equal to the Chinese CPU. However, it may pass some time until someone will build such a big system with MI355X, though perhaps the existence of this new contender might prompt the US labs to upgrade their systems by replacing the older AMD GPUs with newer AMD GPUs.

adrian_b 4mo ago

As I have mentioned, and as described in TFA, this supercomputer is also leading in memory bandwidth (4 TB/s per socket => correction, it is 8 Tb/s per socket). I agree with what you say about benchmarks, but that is precisely why the advantage of this supercomputer over the following American supercomputers will be even greater in more demanding workloads than Linpack and HPCG. It has already shown this by having an advantage in HPCG of greater than 26% over the fastest US system, while in Linpack its advantage is of only 22%. Thus its position in the top cannot be dismissed as insignificant, because it more likely underestimates than overestimates this system. Also the programming effort for writing an efficient program will be lower than for the GPU-based US supercomputers.

jandrewrogers 4mo ago
I definitely appreciate the CPU-centric approach. It appeals to my biases and aligns with my technical perspective. The memory bandwidth is something you can buy. Exotics were >1 TB/s over a decade ago, so 4 TB/s in 2026 is not that impressive. For all practical purposes, these CPUs are also still exotics, you can’t just buy them. I would be very surprised if the memory bandwidth of US exotics haven’t improved over the last 10-15 years. In any case, for real workloads scalability is mostly a software theory problem at this point and that is still a dark art without much literature.
- adrian_b 4mo ago
  Correction, I took the 4 TB/s from TFA, but the NextPlatform article clarifies that it is 4 TB/s per chiplet, but 8 TB/s per socket, so more impressive. The only US-designed CPU "exotics" are the Intel Xeon Max CPU series, which use HBM like the Chinese CPUs, but which have a theoretical maximum throughput of only 1.6 TB/s per socket, i.e. 5 times slower than the new Chinese CPUs. Moreover, the users of Intel Xeon Max complained that they cannot reach the theoretical memory bandwidth. I do not know if that was due to some bug that might have been solved later by Intel with a microcode update or a new mask set stepping. The server CPUs with standard DIMMs, which will be launched by AMD and Intel next year, will have a memory bandwidth of around 1 TB/s per socket. The AMD MI300 GPU used in the fastest US supercomputer has a memory throughput of 5.2 TB/s per socket, so lower than the 8 TB/s per socket of the Chinese CPU, which explains why the advantage of the Chinese system increases in the benchmarks more dependent on memory performance. The latest AMD Instinct GPU, MI355X, increases the memory bandwidth to 8 TB/s, so equal to the Chinese CPU. However, it may pass some time until someone will build such a big system with MI355X, though perhaps the existence of this new contender might prompt the US labs to upgrade their systems by replacing the older AMD GPUs with newer AMD GPUs.