Zen 4 is really bad

By: Adrian (a.delete@this.acm.org), May 26, 2022 5:16 am
Room: Moderated Discussions
-.- (blarg.delete@this.mailinator.com) on May 26, 2022 2:13 am wrote:
> Kara (karaardalan.delete@this.gmail.com) on May 26, 2022 1:52 am wrote:
> > So, is AMD paying everyone to pretend Zen 4 is so awsome? Because Zen 4 numbers look embarrassing.
> > 12% increase in clock speed, 100% increase in L2 cache, and 15% increase in
> > ST perf.? Nah that can't be right, that'd imply Zen 4 is worse, mArch-wise.
> >
> > Or did they pull an Intel/Arm and sacrifice some of the Ex ports for ML pipelines?
> > Or did they pull a cortex A710 and just literally cut off some Ex ports?
> 15% increase in ST perf in what?

It seems that the 15% increase was in the Cinebench ST benchmark.

I mostly agree with the analysis published by Charlie Demerjian at SemiAccurate about the Zen 4 presentation, which I have watched and I have also been disappointed.

The optimists say that maybe AMD has intentionally presented worse results than would be actually obtained in the production units, to mislead the competition, but such a strategy does not make much sense.

As noticed by Charlie and other commentators, the benchmark results shown by AMD are very poor in comparison with what would have been expected after the transition to the superior 5-nm process, which should have allowed a significant increase in the complexity of a Zen 4 core in comparison with a Zen 3 core.

The 15% increase in ST performance, while also showing a 5 to 10% increase in the clock frequency, would mean an increase in IPC of only 5 to 10%.

Zen 3 has a slightly better IPC than Tiger Lake, but with such a small increase in IPC Zen 4 will have a lower IPC than Alder Lake and Raptor Lake.

In that case, Zen 4, which will have about the same single-thread clock frequencies as Alder Lake and Raptor Lake, will have a lower ST performance than them.

The only hope for AMD would be if they could produce in large numbers SKUs with a 5.5 GHz clock frequency, while Intel would continue to be able to mass produce only 5.2 GHz and have 5.5 GHz only in low-volume cherry-picked SKUs.

In the benchmark where AMD has compared Zen 4 with the competition, i.e. MT Blender, there the performance of a Zen 4 SMT thread was equal to the performance of an Alder Lake SMT thread, but presumably at a much lower power consumption, because the turbo power limit for the new AM5 socket is only 2/3 of the power limit of Alder Lake.

Zen 4 will continue the existing situation, where the AMD CPUs win in multi-thread applications mainly because in a power-limited scenario the AMD cores reach a higher clock frequency than the Intel cores. It is likely that the equal performance per thread was due to Alder Lake having a higher IPC, but a lower clock frequency.

While AMD claimed that the 4/3 performance advantage over Alder Lake is a win, that is mainly due because they have compared a 16-big-core CPU with a CPU having the equivalent of only 12 big cores. The competition of Zen 4 will not be Alder Lake, but Raptor Lake, which will increase the number of cores up to the equivalent of 16 big cores, so we can expect that Raptor Lake and Zen 4 will have the same MT performance, but Raptor Lake will have a higher ST performance.

Maybe the optimists are right and AMD might still be fighting some bugs, so they did not want to show better results that are uncertain yet for the products available at launch. After a rather flawless execution of the previous Zen generations, it seems somewhat unlikely that they would have right now an Intel-like flop, when Intel makes serious efforts to leapfrog all the advances made by AMD.

In any case, what I would have liked at the AMD presentation was not to see benchmarks, but to see some commitment for important architectural features.

They have confirmed now a lot of details about the AM5 platform, and those are all good, PCIe5, DDR5, 4 additional PCIe lines for Thunderbolt/USB4 controller, internal GPU in the I/O chip, 4 displays, and so on.

About the core, there was no information at all, besides confirming 8 cores per chiplet and a 5.5 GHz maximum turbo clock frequency.

I would have liked to see a commitment to enable AVX-512 and ECC on all their desktop SKUs. Now, after Intel has enabled ECC on many SKUs from i3 to i9, and they offer a much better software support for it than AMD, it would be stupid for AMD to regress, but you never know.

The same applies to AVX-512, when AMD has always had the competitive advantage of not disabling features on the cheaper SKUs, it would be stupid to have AVX-512 on Epyc and disable it on Ryzen, but AMD has avoided until now to say anything about this.

They have mentioned "new instructions for ML & AI", but that could mean anything. I do not care about "ML & AI", which I can do on GPUs, I care about computations with double-precision FP numbers and computations with large numbers, which can no longer be done effectively on cheap GPUs, since both NVIDIA and AMD have different "gaming" and "datacenter" architectures, with the latter being much more expensive than CPUs. Therefore, I care about the base AVX-512 ISA and about a part of the later extensions, like IFMA.

It appears that we will not know what ISA is implemented by Zen 4, until a few days after launch, when some kind soul will publish the content of /proc/cpuinfo.

Until Zen, both AMD and Intel published with 1 or more years in advance their future ISAs, to give time to the software developers to prepare for them.

Intel continues to publish such information, but since the first Zen, AMD has stopped publishing complete information before the launch, and even after the launch a long time may pass until having adequate documentation about a new Zen generation.

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TopicPosted ByDate
Zen 4 is really badKara2022/05/26 01:52 AM
  Zen 4 is really bad-.-2022/05/26 02:13 AM
    who is the champ right now?Michael S2022/05/26 03:36 AM
      who is the champ right now?Kara2022/05/26 04:16 AM
        Alder lake better than zen4!Kara2022/05/26 04:24 AM
          Alder lake better than zen4!Adrian2022/05/26 05:40 AM
            Alder lake better than zen4!anon22022/05/26 06:14 PM
              Alder lake better than zen4!Adrian2022/05/27 04:18 AM
                Alder lake better than zen4!Matt Hughes2022/05/28 11:15 PM
      who is the champ right now?-.-2022/05/26 05:23 AM
        who is the champ right now?Adrian2022/05/26 06:09 AM
          who is the champ right now?Andrei F2022/05/26 06:16 AM
            who is the champ right now?Adrian2022/05/26 07:10 AM
              who is the champ right now?Andrei F2022/05/26 07:37 AM
                who is the champ right now?Andrei F2022/05/26 07:59 AM
              who is the champ right now?Eric Fink2022/05/27 12:17 AM
                who is the champ right now?Adrian2022/05/27 05:41 AM
            Optimally?Anon2022/05/26 09:43 AM
              Optimally?Andrei F2022/05/26 12:10 PM
          who is the champ right now?-.-2022/05/26 06:43 PM
            who is the champ right now?Adrian2022/05/27 05:24 AM
          Nothing wrong with anads spec2006 results - see the breakdownHeikki Kultala2022/05/27 03:23 PM
            Nothing wrong with anads spec2006 results - see the breakdownDoug S2022/05/27 09:59 PM
              Nothing wrong with anads spec2006 results - see the breakdownMatt Hughes2022/05/28 06:32 PM
                Nothing wrong with anads spec2006 results - see the breakdownMichael S2022/05/29 01:44 AM
                  Nothing wrong with anads spec2006 results - see the breakdownAdrian2022/05/29 03:53 AM
    Zen 4 is really badAdrian2022/05/26 05:16 AM
      Zen 4 is really bad-.-2022/05/26 05:58 AM
        Zen 4 test conditionsAdrian2022/05/26 06:14 AM
          Zen 4 test conditionsGroo2022/05/26 06:01 PM
        Zen 4 ECCAdrian2022/05/26 06:33 AM
          Zen 4 ECC-.-2022/05/26 06:38 PM
            Zen 4 ECCAdrian2022/05/27 05:11 AM
              Zen 4 ECC-.-2022/05/27 08:30 PM
                Zen 4 ECCMichael S2022/05/28 11:19 AM
          Zen 4 ECCdrAgonear2022/05/26 11:58 PM
            Zen 4 ECCDavid Hess2022/05/30 07:29 PM
      Zen 4 is really badgoose2022/05/26 08:14 PM
        Zen 4 is really badAdrian2022/05/27 04:44 AM
          Zen 4 is really badJames2022/05/27 06:13 AM
  Zen 4 is really badJohn H2022/05/26 05:45 AM
  Zen 4 is really badDoug S2022/05/26 10:50 AM
    Zen 4 is really badDummond D. Slow2022/05/28 09:14 PM
      Zen 4 is really badDoug S2022/05/29 09:49 AM
  Please check the faxts instead of posting crap like thisHeikki Kultala2022/05/26 11:05 AM
    Zen 4 IPC2022/05/26 11:24 AM
      Zen 4 IPC and AVX-512Per Hesselgren2022/05/27 01:07 AM
        Zen 4 IPC and AVX-512Per Hesselgren2022/05/27 03:44 AM
        Zen 4 IPC and AVX-512Adrian2022/05/27 04:57 AM
          Zen 4 IPC and AVX-512anon2022/05/27 08:22 AM
  Zen 4 is really badParsnip2022/05/29 04:20 AM
    What do you mean by 3-wide desing?Heikki Kultala2022/05/29 01:05 PM
      What do you mean by 3-wide desing?Doug S2022/05/29 02:32 PM
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