Some 'reverse-engineering' of Zen

By: juanrga (, November 2, 2015 5:06 am
Room: Moderated Discussions
Maynard Handley ( on November 1, 2015 6:33 pm wrote:
> juanrga ( on November 1, 2015 8:16 am wrote:
> > Poindexter ( on October 31, 2015 5:37 pm wrote:
> > > lurker (lurker9000.delete@this.realemail.mail) on October 31, 2015 4:06 pm wrote:
> > > > Poindexter ( on October 31, 2015 2:47 pm wrote:
> > > > > I find it funny that you like to tout pipe numbers, but you never discuss
> > > > > other architectural features that have direct impact in this discussion:
> > > > > - MOV elimination
> > > > > - Store-to-load forwarding
> > > > > - Memory reordering and memory disambiguation
> > > > > - Instruction fusing
> > > >
> > > > I think the point is that we don't really know the details on the rest of the architecture?
> > > > So I think it's not a problem if he focuses on the details we do know.
> > >
> > > Yeah, but to assert that the architecture is unbalanced just by looking at the number of ports,
> > > doing some back-of-the-envelope math about it, without access to a single simulation, is just a
> > > *bit* too far, don't you think? Makes it look like every AMD engineer is plain incompetent.
> > >
> > > > > - Never provided any connection between Haswell's increased IPC over Ivy Bridge to the third AGU.
> > > >
> > > > I have no idea if this is the reason for it, but in Haswell SMT works a lot better than in Ivy.
> > > > Say if you were doing multi-core compilation in Ivy, the whole system would just freeze up until
> > > > the work is completed. It seems to be a bit better in Haswell so perhaps that extra AGU helps?
> > >
> > > Sure it helps. Then again Haswell also got a new issue port for ALU operations, including a branch
> > > unit which might also help during SMT compilation. Which one is the most important? I don't know!
> > >
> > > > > Regarding the FPU, you never mention that Zen's FPU doesn't share ports with the integer ALUs like
> > > > > Haswell does. You never mention that Zen's FPU has more ports and units than Haswell's. You only seem
> > > > > to care about maximum throughput (in the e-penis sense), which frankly, is not that interesting.
> > > >
> > > > Is it really that much of an advantage that FPU doesn't share ports with interger ALUs? In SMT perhaps?
> > > > I guess the separate ports for the ADD and MUL units are an advantage in some workloads.
> > > > And to be fair maximum throughput is important in HPC, right? I
> > > > don't think it's that important in general workloads though.
> > >
> > > Having separate ports is certainly an advantage. Just like
> > > Haswell's third AGU is. The tricky part is how you
> > > quantify this advantage, how you compare those features. With the information we have, it's impossible.
> > >
> > > Throughput is important for HPC, that's true, but juan condemned Zen in all markets.
> >
> > Because Zen looks inferior to competence in any metric?
> >
> > > In HPC's case, the lack of AVX-512 has vastly more influence in Zen's ability to get into those
> > > HPC supercomputers than a missing AGU (then again, it wasn't long ago that he was saying that
> > > ARMs were better than Haswells when driving HPC GPUs, same perf, lower power, but I guess he
> > > changed his mind about it). We can't really conclude anything about any market.
> > >
> > > I just did some static instruction count on LAPACK (default package on Ubuntu) - it doesn't use
> > > packed AVX instructions and it's full of LEAs (think it's due Fortran's calling convention). Looks
> > > just the kind of code where Zen's FPU can issue 4 instructions per cycle while the integer side
> > > is also on full tilt. Zen may be much better than Haswell for scientific computing.
> >
> > The ratio 1:2 for mem:FP is not the ideal for scientific computing. Zen will be inferior
> > to Haswell/Broadwell, Power8, and very inferior to Skylake (Xeon), KNL Phi, XIfx,...
> >
> > > It also may be great for office work, for laptops, games, all kinds of web servers, so on and so forth.
> >
> > 90% of people don't need to purchase Zen for desktop office work, because will not boost applications over
> > existent products and for the rest there are other products in the market as well. Laptops don't use 8-core
> > CPUs, and when first Zen-based APUs arise, Kabylake will be on market and Canonlake close to release.
> There's a bizarre sort of unreality to this whole discussion.
> 90% of people don't give a damn what CPU they buy. They go to Best Buy and choose the laptop that seems
> right to them, which is some combination of mostly price and the rest packaging and appearance.
> Which means how Zen does is driven by its cost and its strengths/weaknesses
> (and so where Dell, HP, Lenovo etc use it in their lineups).
> What the average person thinks of the CPU doesn't matter in the slightest. What matters is the performance/dollar
> (so can the manufacturers move it to higher tier machines) and the battery life under Windows 10
> (so can the manufacturers boast about that or have to hide it shamefully).
> The ONLY point at which 2 AGUs:4 ALUs matters is if they exceed Intel single-threaded performance
> and the 1% of people who actually care about CPUs want to investigate how they did it. Since exceeding
> Intel performance seems highly unlikely, this is not a point that actually matters.
> For everyone else, this is all driven by ECONOMICS, not functional unit ratios. Assuming basic competence
> (a hell of an assumption with AMD, but still), the CPU will get into HPC (or not) and laptops (or not)
> based on its price and its energy efficiency, the two variables that are not being discussed here.

I think Zen will be expensive because (i) there are many more transistors than Excavator, (ii) the FinFET node is not cheap, and (iii) AMD needs the money.

I think AMD will be behind in efficiency, unless drops clocks enough to compensate.
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TopicPosted ByDate
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                      Some 'reverse-engineering' of ZenGabriele Svelto2015/10/30 03:14 AM
                        Some 'reverse-engineering' of Zenlurker2015/10/30 03:41 AM
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                          Some 'reverse-engineering' of Zenjuanrga2015/10/30 01:00 PM
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                              AVX and 128-bit FPUs in Zen(Re:Some 'reverse-engineering' of Zen)juanrga2015/10/31 06:20 AM
                                AVX and 128-bit FPUs in Zen(Re:Some 'reverse-engineering' of Zen)Heikki Kultala2015/10/31 02:19 PM
                                  AVX and 128-bit FPUs in Zen(Re:Some 'reverse-engineering' of Zen)juanrga2015/11/01 07:41 AM
                                    AVX and 128-bit FPUs in Zen(Re:Some 'reverse-engineering' of Zen)Anne O. Nymous2015/11/01 09:39 AM
                                AVX and 128-bit FPUs in Zen(Re:Some 'reverse-engineering' of Zen)Matthias Waldhauer2015/11/02 01:26 PM
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                            Some 'reverse-engineering' of ZenMatthias Waldhauer2015/11/02 11:39 AM
                        Some 'reverse-engineering' of Zenbakaneko2015/10/31 07:28 AM
                          Some 'reverse-engineering' of Zendmcq2015/10/31 08:19 AM
                            Some 'reverse-engineering' of ZenJukka Larja2015/10/31 09:21 AM
                            Some 'reverse-engineering' of Zenbakaneko2015/10/31 10:23 AM
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                              Some 'reverse-engineering' of Zenlurker2015/10/31 04:06 PM
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                                  Some 'reverse-engineering' of Zenlurker2015/11/01 03:46 AM
                                  Some 'reverse-engineering' of Zenjuanrga2015/11/01 08:16 AM
                                    Some 'reverse-engineering' of ZenMaynard Handley2015/11/01 06:33 PM
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                                            Some 'reverse-engineering' of ZenJukka Larja2015/11/03 02:41 AM
                                              Some 'reverse-engineering' of Zennobody2015/11/03 05:10 AM
                                                Some 'reverse-engineering' of ZenJukka Larja2015/11/04 02:52 AM
                                            Some 'reverse-engineering' of ZenKlimax2015/11/03 02:47 AM
                                              Some 'reverse-engineering' of Zennobody2015/11/03 04:19 AM
                                                Some 'reverse-engineering' of ZenKlimax2015/11/03 12:09 PM
                                          Some 'reverse-engineering' of ZenBanana_Comedown2015/11/04 11:17 AM
                                            Some 'reverse-engineering' of ZenJukka Larja2015/11/05 03:51 AM
                                              Some 'reverse-engineering' of ZenBanana_Comedown2015/11/05 01:23 PM
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                                Some 'reverse-engineering' of Zennobody2015/10/31 08:16 PM
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                                    Some 'reverse-engineering' of Zensylt2015/11/01 04:07 AM
                                    Some 'reverse-engineering' of Zennobody2015/11/01 11:49 AM
                                  Some 'reverse-engineering' of Zenmd2015/11/01 01:06 PM
                                    Some 'reverse-engineering' of Zenblu2015/11/01 01:59 PM
                                      Some 'reverse-engineering' of Zenjuanrga2015/11/02 05:10 AM
                              Some 'reverse-engineering' of Zenjuanrga2015/11/01 07:00 AM
                                Some 'reverse-engineering' of ZenPoindexter2015/11/01 09:25 AM
                                  Some 'reverse-engineering' of Zenjuanrga2015/11/02 04:47 AM
                                    Some 'reverse-engineering' of ZenPoindexter2015/11/02 05:39 AM
                                      Some 'reverse-engineering' of Zenjuanrga2015/11/02 01:26 PM
                                        Some 'reverse-engineering' of ZenDan Downs2015/11/02 03:12 PM
                                          Some 'reverse-engineering' of Zenjuanrga2015/11/03 03:51 AM
                            Some 'reverse-engineering' of Zenlurker2015/10/31 03:57 PM
                              Some 'reverse-engineering' of Zenjuanrga2015/11/01 07:26 AM
                                Some 'reverse-engineering' of ZenHeikki Kultala2015/11/01 09:57 AM
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                  Some 'reverse-engineering' of Zenquzhujian2015/10/31 10:39 AM
                  Some 'reverse-engineering' of ZenPoindexter2015/11/04 06:10 AM
                    Some 'reverse-engineering' of Zenlurker2015/11/05 01:54 PM
                      Some 'reverse-engineering' of Zennobody2015/11/05 03:28 PM
                      The sad status of tech mediajuanrga2015/11/06 05:19 AM
                        The sad status of tech mediaJoel2015/11/06 06:45 PM
                        The sad status of tech mediaMatthias Waldhauer2015/11/07 03:12 PM
                          The sad status of tech mediaJoel2015/11/07 05:40 PM
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