[blopeur]

A64fx have on board HMB -> that means no dram. If you look at the fugaku mother board their is no Dimm slots. All the memory is on the same package as the CPU.

This delivers a huge boost in bandwith.

HMB stand for high memory bandwidth. It offers up to 900 GB/s.

Now if you add the tofu interconnect on top you have a systems finely tuned for maximising data movement.

Remember : compute is cheap, communication is expensive.

You can have load of gpu and processors but if you can't feed them data fast enough they are useless.

[blopeur]

For a more in depth dive :

"Report on the Fujitsu Fugaku (富岳) System", Jack Dongarra, Jun 22, 2020

https://www.dropbox.com/s/aqntdb43p6so0z5/fugaku-report.pdf?...

[ViralBShah]

That is a pretty fun architecture. I hope that opens the door to higher performance for more workloads than top500.

At least with the top500 benchmark, the bandwidth is not a problem, so long as you can do a large enough problem. Since it is a linear solve that spends all its time doing matmul (n^3 operations on n^2 data), so long as the problem is big enough, you can saturate the cores.

[lukevp]

That's fascinating. I know that AMD has been touting HBM as a faster memory subsystem for their GPUs, is that the same as HMB where it's stacked? Or are they just calling it something similar?

[rrss]

It's the same thing. High end GPUs have been using HBM2 for a few years, A64fx uses HBM2 for CPU memory.

[floatboth]

"HMB" is a typo, it is the same HBM.

And yeah.. honestly I'm surprised AMD didn't do the HBM-CPU thing first. An HBM2-powered EPYC would've been an amazing product.