Some 'reverse-engineering' of Zen

By: juanrga (nospam.delete@this.juanrga.com), November 1, 2015 7:26 am
Room: Moderated Discussions
lurker (lurker9000.delete@this.realemail.mail) on October 31, 2015 3:57 pm wrote:
> juanrga (nospam.delete@this.juanrga.com) on October 31, 2015 12:50 pm wrote:
> > We know the claimed IPC for Zen
>
> I don't think IPC was the big problem for bulldozer. I think the problem was other
> bottlenecks. At least I remember reading an article about it on anandtech I think
> where it was compared to jaguar. And very poor FP performance of course.
>
> > we know Papermaster admitted @ FAD 2015 that it is not enough to match Intel
>
> Really? I honestly don't remember that.

In the Q&A yesterday an analyst pointed out that a 40% IPC increase wouldn't close the performance gap with Intel. Papermaster's response is that it would be enough to put AMD "that zone of competitiveness that we need to compete in the markets". Basically it is an admission Zen will not be as fast as Skylake core-for-core, and gives AMD enough wiggle room to launch Zen with Sandy/Ivy Bridge level of performance/MHz.


> > we know AMD will use a 14nm node that will not hit clocks so high as Intel 14nm;
>
> Sure that's a safe guess, intel has a high-performance optimized node and samsung/global foundries have
> a low-power optimized node. But I think that's really only important in high-end desktop processors.
>
> > 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...
>
> Yes, but as I previously asked wouldn't at least disabling it save some power and heat?
> If it's there it means it is not completely useless, right? I'm not expert at hardware
> so I'm not sure if just disabling it actually helps, sorry if this is a dumb question.

As said above maybe it is here for "symmetry reasons". Zen design is highly symmetric with each execution unit coming in pairs. I suspect that AMD is not enabling full SMT on Zen, but a partial CSMT implementation. If this is true Zen is a simple clustered design and the fourth ALU is here because both clusters have to be the identical for simplifying thread selection and scheduling.
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TopicPosted ByDate
Some 'reverse-engineering' of Zenjuanrga2015/10/03 04:48 AM
  Some 'reverse-engineering' of ZenHeikki Kultala2015/10/03 08:01 AM
    Some 'reverse-engineering' of Zenitsmydamnation2015/10/03 03:47 PM
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        Some 'reverse-engineering' of ZenContrarian2015/10/04 11:53 AM
          Some 'reverse-engineering' of ZenJukka Larja2015/10/05 09:15 AM
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                    Some 'reverse-engineering' of Zenjuanrga2015/10/30 10:37 AM
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                    Some 'reverse-engineering' of Zenlurker2015/10/30 02:39 AM
                      Some 'reverse-engineering' of ZenGabriele Svelto2015/10/30 03:14 AM
                        Some 'reverse-engineering' of Zenlurker2015/10/30 03:41 AM
                      Some 'reverse-engineering' of Zendmcq2015/10/30 05:12 AM
                        Some 'reverse-engineering' of Zenlurker2015/10/30 05:56 AM
                          Some 'reverse-engineering' of Zendmcq2015/10/30 06:09 AM
                            Some 'reverse-engineering' of Zennone2015/10/30 06:16 AM
                          Some 'reverse-engineering' of ZenDavid Kanter2015/10/30 08:16 AM
                            Some 'reverse-engineering' of Zenlurker2015/10/30 08:44 AM
                          Some 'reverse-engineering' of Zenjuanrga2015/10/30 01:00 PM
                            AVX and 128-bit FPUs in Zen(Re:Some 'reverse-engineering' of Zen)Heikki Kultala2015/10/30 03:45 PM
                              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
                                  AVX and 128-bit FPUs in Zen(Re:Some 'reverse-engineering' of Zen)juanrga2015/11/03 03:42 AM
                            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
                              Some 'reverse-engineering' of Zendmcq2015/10/31 04:12 PM
                                Some 'reverse-engineering' of Zenbakaneko2015/10/31 05:25 PM
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                                      Some 'reverse-engineering' of Zendmcq2015/11/01 10:27 AM
                                        Some 'reverse-engineering' of Zenbakaneko2015/11/01 03:35 PM
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                                            Some 'reverse-engineering' of Zenbakaneko2015/11/03 03:17 AM
                                              Some 'reverse-engineering' of Zendmcq2015/11/03 04:17 AM
                  Some 'reverse-engineering' of Zenjuanrga2015/10/30 12:43 PM
                    Some 'reverse-engineering' of Zenlurker2015/10/30 02:09 PM
                      Some 'reverse-engineering' of Zenjuanrga2015/10/31 06:58 AM
                        Some 'reverse-engineering' of Zenlurker2015/10/31 08:07 AM
                          Some 'reverse-engineering' of Zenjuanrga2015/10/31 12:50 PM
                            Some 'reverse-engineering' of ZenPoindexter2015/10/31 02:47 PM
                              Some 'reverse-engineering' of Zenlurker2015/10/31 04:06 PM
                                Some 'reverse-engineering' of ZenPoindexter2015/10/31 05:37 PM
                                  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
                                      Some 'reverse-engineering' of Zenjuanrga2015/11/02 05:06 AM
                                        Zen transistor countHeikki Kultala2015/11/04 01:30 AM
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                                    Some 'reverse-engineering' of ZenSymmetry2015/11/02 06:56 AM
                                      Some 'reverse-engineering' of ZenDavid Hess2015/11/02 07:16 AM
                                      Some 'reverse-engineering' of Zennobody2015/11/02 08:19 AM
                                        Some 'reverse-engineering' of ZenJukka Larja2015/11/02 09:34 PM
                                          Some 'reverse-engineering' of Zennobody2015/11/03 01:35 AM
                                            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
                                      Some 'reverse-engineering' of Zenjuanrga2015/11/03 04:13 AM
                                Some 'reverse-engineering' of Zennobody2015/10/31 08:16 PM
                                  Some 'reverse-engineering' of Zenlurker2015/11/01 03:48 AM
                                    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
                                  Some 'reverse-engineering' of ZenMaynard Handley2015/11/01 06:39 PM
                              Some 'reverse-engineering' of ZenUngo2015/11/01 02:05 PM
                  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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