Neat die area comparison image

By: Maynard Handley (name99.delete@this.name99.org), October 24, 2016 4:27 pm
Room: Moderated Discussions
Travis (travis.downs.delete@this.gmail.com) on October 24, 2016 1:26 pm wrote:
> David Hess (davidwhess.delete@this.gmail.com) on October 22, 2016 1:26 pm wrote:
> > But it only does this at half of the clock rate. Skylake has a 4 cycle load latency which pipelining
> > and out of order execution neatly hide. The A10 probably has the same 4 cycle load latency that
> > the A9 has but at twice the clock rate, that would become an unsustainable 8 cycles meaning that
> > the core would be spending half of its time waiting lowering its IPC by a factor of 2.
>
> I'm confused by your claim that the 4 cycle latency on Intel is hidden by "which pipelining
> and out of order execution", but that a latency of 8 cycles would halve the IPC?
>
> There is nothing magic about a load-to-use latency of 4. Whether a bit of code is limited by this latency
> depends entirely on the code. Sometimes this latency is hidden, and often it is not (many types of
> pointer chasing or table lookup codes end up being limited by the L1 cache latency in practice). If
> the latency was 3, it could be hidden (or partially hidden) a bit more often and improve performance
> slightly. If it was 5, it would be hidden (or partially hidden) a bit less and performance would suffer
> a bit. If load-to-use latency jumped to 8, it would impact performance - but only on the most pathological
> cases would it halve performance (codes that are entirely L1 latency bound).

There's also an assumption being made that the engineering causality was:
try to make loads as fast as possible -> Apple can only get the latency down to 4 @ 2.35GHz

The more likely chain of engineering causality was:
what's the best latency vs energy tradeoff for what we're designing? -> design for a latency of 4.

The point is, the first model assumes engineering incapable of designing a lower latency load-store-cache system; the second assumes engineering optimized for the task at hand. There's less evidence to assume the first than to assume the second.

Beyond this, the naive model suggested by David Hess assumes the A10 is clocked at maximum frequency for this design. This is highly unlikely. We'll see a higher frequency limit when the A10X ships. You all know the frequency I've suggested that could be clocked at, based simply on the A9X vs A9 frequency scaling, and what TSMC has said about their 10nm process, but scaling that to beyond 4GHz it seems reasonable to say that Apple's current design would engender something more like 5 rather than 8 clocks.
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TopicPosted ByDate
Neat die area comparison imageRob2016/10/21 05:39 PM
  Neat die area comparison imageanonymou52016/10/21 06:44 PM
    Neat die area comparison imageMr. Camel2016/10/22 04:58 AM
      Neat die area comparison imageHeikki Kultala2016/10/22 05:19 AM
        Neat die area comparison imageMr. Camel2016/10/22 07:10 AM
          Neat die area comparison imageMr. Camel2016/10/22 07:15 AM
          different caches...Heikki Kultala2016/10/22 08:29 AM
            Broadwell includes LLC, just for comparisionanon2016/10/22 08:52 AM
              Broadwell includes LLC, just for comparisionjuanrga2016/10/23 06:09 AM
                Broadwell includes LLC, just for comparisionanon2016/10/23 07:25 AM
                  Broadwell includes LLC, just for comparisionjuanrga2016/10/25 09:57 AM
                    Broadwell includes LLC, just for comparisionSimon Farnsworth2016/10/25 11:03 AM
                      Broadwell includes LLC, just for comparisionjuanrga2016/10/28 02:02 AM
                        Broadwell includes LLC, just for comparisionanon2016/10/28 04:13 AM
                          Broadwell includes LLC, just for comparisionjuanrga2016/10/29 09:47 PM
                            Broadwell includes LLC, just for comparisionTravis2016/10/30 06:34 PM
                              Broadwell includes LLC, just for comparisionjuanrga2016/10/31 04:35 AM
                                Broadwell includes LLC, just for comparisionSimon Farnsworth2016/10/31 04:42 AM
                                Broadwell includes LLC, just for comparisionanon2016/11/01 12:56 PM
                                  Broadwell includes LLC, just for comparisionMaynard Handley2016/11/01 01:37 PM
                                    Broadwell includes LLC, just for comparisionanon2016/11/01 04:22 PM
                                      Broadwell includes LLC, just for comparisionMaynard Handley2016/11/01 07:30 PM
                                        Broadwell includes LLC, just for comparisionanon2016/11/02 06:15 AM
                                          Broadwell includes LLC, just for comparisionMaynard Handley2016/11/02 09:23 AM
                                            Broadwell includes LLC, just for comparisionanon2016/11/02 11:50 AM
                                  Broadwell includes LLC, just for comparisionSimon Farnsworth2016/11/02 02:48 AM
                        Broadwell includes LLC, just for comparisionSimon Farnsworth2016/10/28 06:19 AM
                          Broadwell includes LLC, just for comparisionjuanrga2016/10/29 10:15 PM
                            Broadwell includes LLC, just for comparisionSimon Farnsworth2016/10/30 12:31 PM
                        Broadwell includes LLC, just for comparisionRicardo B2016/10/29 05:30 PM
                    underclocked is different than designed for low clock speedHeikki Kultala2016/10/25 11:47 PM
                      underclocked is different than designed for low clock speedMaynard Handley2016/10/26 10:07 AM
                      That wasn't the pointjuanrga2016/10/28 02:15 AM
                        Even without the point you have invalid comparisonHeikki Kultala2016/10/28 09:03 AM
                          8 wide vs 6 widejuanrga2016/10/29 10:41 PM
                            8 wide vs 6 wideWilco2016/10/30 05:00 AM
                              8 wide vs 6 wideDoug S2016/10/30 12:20 PM
                                8 wide vs 6 wideWilco2016/10/30 01:12 PM
                                8 wide vs 6 widejuanrga2016/10/30 02:56 PM
                                  8 wide vs 6 wideTravis2016/10/30 07:13 PM
                                    8 wide vs 6 widejuanrga2016/10/31 04:55 AM
                                      8 wide vs 6 wideanon2016/11/01 01:00 PM
                                        SoftMachinesnone2016/11/02 03:57 AM
                                          SoftMachinesDavid Kanter2016/11/02 08:53 AM
                                        8 wide vs 6 widejuanrga2016/11/03 12:35 PM
                                          8 wide vs 6 wideWilco2016/11/03 02:13 PM
                                            8 wide vs 6 widejuanrga2016/11/03 07:35 PM
                                              8 wide vs 6 wideWilco2016/11/04 01:27 PM
                                                8 wide vs 6 widejuanrga2016/11/04 06:08 PM
                                                  8 wide vs 6 wideWilco2016/11/06 04:52 AM
                                                    8 wide vs 6 widejuanrga2016/11/06 04:56 PM
                                                      8 wide vs 6 wideWilco2016/11/07 04:25 AM
                                              8 wide vs 6 wideAaron Spink2016/11/04 04:08 PM
                                                8 wide vs 6 widejuanrga2016/11/04 06:10 PM
                                            Dunning-Krueger effectHeikki Kultala2016/11/04 03:22 AM
                                              Dunning-Krueger effectitsmydamnation2016/11/04 02:48 PM
                                          8 wide vs 6 wideanon2016/11/04 03:38 AM
                                            8 wide vs 6 widejuanrga2016/11/04 05:05 AM
                                              8 wide vs 6 wideanon2016/11/04 06:12 AM
                                                8 wide vs 6 wideWilco2016/11/04 01:12 PM
                                                  8 wide vs 6 wideanon2016/11/04 02:54 PM
                                                    8 wide vs 6 widejuanrga2016/11/04 05:34 PM
                                                      8 wide vs 6 wideanon2016/11/05 02:14 AM
                                                  8 wide vs 6 widejuanrga2016/11/04 05:39 PM
                                                    8 wide vs 6 wideWilco2016/11/06 05:15 AM
                                                      8 wide vs 6 widejuanrga2016/11/06 05:06 PM
                                                        8 wide vs 6 wideWilco2016/11/07 03:45 AM
                                                          8 wide vs 6 wideDavid Kanter2016/11/07 08:43 PM
                                                            8 wide vs 6 wideWilco2016/11/08 03:57 AM
                                                          8 wide vs 6 widejuanrga2016/11/14 12:12 PM
                                                            8 wide vs 6 wideWilco2016/11/14 04:53 PM
                                                              8 wide vs 6 widedmcq2016/11/15 03:17 AM
                                                                8 wide vs 6 wideWilco2016/11/15 03:43 AM
                                                                  8 wide vs 6 widedmcq2016/11/15 04:28 AM
                                                                  1 µop per instruction is not necessaryPaul A. Clayton2016/11/17 12:09 PM
                                                              8 wide vs 6 widejuanrga2016/11/20 06:56 AM
                                                                8 wide vs 6 wideWilco2016/11/21 05:54 PM
                                                                  8 wide vs 6 widejuanrga2016/11/22 08:49 AM
                                                                    8 wide vs 6 wideWilco2016/11/22 03:25 PM
                                  8 wide vs 6 wideWilco2016/10/31 03:03 AM
                              Skylake can retire 8 uopsDavid Kanter2016/10/31 12:41 AM
                                Skylake can retire 8 uopsjuanrga2016/10/31 04:15 AM
                                  Skylake can retire 8 uopsAlberto2016/11/04 07:22 AM
                            8 wide vs 6 wide bogus numbersHeikki Kultala2016/10/30 06:25 AM
                    Broadwell includes LLC, just for comparisionanon2016/10/26 03:10 AM
                      Pushing the hidden agendajuanrga2016/10/28 03:11 AM
                        Pushing the hidden agendaanon2016/10/28 04:35 AM
      Neat die area comparison imageDavid Hess2016/10/22 01:26 PM
        Neat die area comparison imageanon22016/10/22 05:20 PM
          Neat die area comparison imageDavid Hess2016/10/22 10:31 PM
            Neat die area comparison imageanon22016/10/23 01:50 AM
        Neat die area comparison imageTravis2016/10/24 01:26 PM
          Neat die area comparison imageMaynard Handley2016/10/24 04:27 PM
            Neat die area comparison imagejuanrga2016/10/25 10:02 AM
            Neat die area comparison imageDavid Hess2016/10/25 09:59 PM
              Neat die area comparison imageTravis2016/10/25 10:22 PM
                Neat die area comparison imageDavid Hess2016/10/25 10:37 PM
                  Neat die area comparison imageTravis2016/10/30 06:09 PM
              Neat die area comparison imageGabriele Svelto2016/10/26 02:23 AM
                Neat die area comparison imageDoug S2016/10/26 08:17 AM
                  Neat die area comparison imageJukka Larja2016/10/27 09:28 AM
              Neat die area comparison imageanon2016/10/26 03:32 AM
      Neat die area comparison imagejuanrga2016/10/23 06:29 AM
    Neat die area comparison imageMatthias Waldhauer2016/10/22 06:12 AM
  Neat die area comparison imagejuanrga2016/10/23 05:44 AM
  Neat die area comparison imageGabriele Svelto2016/10/24 02:17 AM
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