lurker (lurker9000.delete@this.realemail.mail) on October 31, 2015 8:07 am wrote:
> juanrga (nospam.delete@this.juanrga.com) on October 31, 2015 6:58 am wrote:
> >
> > I tried to explain that what matters is not the total number of memory units
> > but the ratio between different execution units, the ISA, and the workloads.
> >
> > As explained before 2AGU+4ALU looks fine for ARM mobile SoC. 2AGU+4ALU looks unbalanced for x86 server SoC.
> >
> > Same stuff about HPC. A third AGU is not obligatory for HPC. Intel's Borkar just gave a recent
> > talk about his vision for a future supercomputer much faster than actual. The HPC core that he
> > proposes has only one AGU, and that is fine because his core has a 1:1 ratio for FP:mem.
> >
> > Fujitsu presented this year the new CPU that will replace the old CPU in the successful
> > K-computer. This new CPU, the XIfx, is exclusively optimized for HPC and each
> > core has 2 AGUs. Again fine because it has a 1:1 ratio for FP:mem...
> >
> > But this discussion about HPC is rather irrelevant, because we know
> > that AMD will not use CPUs for HPC. AMD will propose HSA APUs.
> >
> > About markets Zen can win back easier. I know none. I am rather convinced that HPC Zen-based APUs
> > will fail. Zen on AM4 APUs for desktop/mobile will be too late and competing against Kabylake/Cannonlake.
> > Zen AM4 for CPUs will be competing with Skylake-E CPUs for a niche market: HEDT. And I guess Zen on
> > servers will be crushed by both sides: ARM (Qualcomm, Broadcom, APM,...) and x86 (Intel).
>
> I wouldn't be so negative before it's even released(or before we have some sort of performance indicators
> for it). There's a bunch of engineers with a lot of experience at AMD after all, I'm sure there's a reason
> why it's 2AGU+4ALU and not 3+3 or 2+3. What's the point of 4ALUs if one or two of them will remain idle?
> I'd imagine that extra ALUs, even when not fully utilized, would suck up a lot of power and generate more
> heat. Wouldn't getting rid of it, or at least disabling it, give better performance/watt?

I think I am being simply realist. We know the claimed IPC for Zen; we know Papermaster admitted @ FAD 2015, that it is not enough to match Intel; we know AMD will use a 14nm node that will not hit clocks so high as Intel 14nm; we know AMD lose the moar core advantage on HEDT...

I am sure the reason for 4ALU+2AGU and 128bit FP pipes is not because it is the best possible configuration. The real reason? We only can speculate at this time. Maybe a cache bottleneck did make adding a third AGU useless, maybe the fourth ALU is here for symmetry reasons, maybe...