Infinity Fabric = PCIe

By: Aaron Spink (aaronspink.delete@this.notearthlink.net), March 17, 2017 6:27 pm
Room: Moderated Discussions
Ricardo B (ricardo.b.delete@this.xxxxx.xx) on March 17, 2017 6:08 pm wrote:
> Aaron Spink (aaronspink.delete@this.notearthlink.net) on March 17, 2017 10:25 am wrote:
> > Gabriele Svelto (gabriele.svelto.delete@this.gmail.com) on March 17, 2017 3:35 am wrote:
> > > Michael S (already5chosen.delete@this.yahoo.com) on March 16, 2017 2:33 pm wrote:
> > > > Of course, you are correct. There is only one clock pair per 20 data pairs. It's true
> > > > for all generations of Xeons taht I checked, from Gainstown and up to IvyBridge-EX.
> > >
> > > That is... remarkable at the GT/s they support.
> >
> > The reality is that QPI is not a traditional clk_fwd design. In a lot of ways, QPI electrical
> > is more similar to an AC coupled embedded clock system. Actually using embedded clocks has
>
> I guess it has adjustable delay lines on each data line,
> and the data transitions are used to adjust the delay?
>

Pretty much any high speed receiver is going to have effectively adjustable delay lines for clocking the data. In addition, as you move to higher speeds you also have to dynamically adjust for both drift and jitter over time. The alternative is that you pretty much end up with a separate coupled clk_fwd per data as you increase frequency and db loss.

Effectively QPI drops the embedded clk + clk_gen circuit in a traditional encoded SERDES by using a separate fwd_clk. A lot of the rest of the circuits have to end up being pretty much the same as a traditional SERDES. The trade-off is that you likely can't get as fast as traditional SERDES signalling but due have much more latency savings and flexability along with roughly the same amount of overhead (less overhead than 8/10, more overhead than 64/66 or 128/130, ~5% vs 25%, 3.1% and 1,5% respectively). Latency wise, QPI has a 4 Phit delay, 8/10 a 10 Phit delay, etc. Indications are that QPI_next will go to a wider default width which will lower bandwidth overhead closer to 64/66.
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TopicPosted ByDate
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          What is infinity fabric?Brendan2017/03/14 05:28 AM
            What is infinity fabric?Ireland2017/03/14 06:09 AM
            What is infinity fabric?Groo2017/03/14 07:35 AM
              What is infinity fabric?Ireland2017/03/14 08:35 AM
    Infinity Fabric = PCIeslacker2017/03/15 02:59 PM
      Infinity Fabric = PCIeMichael S2017/03/15 04:19 PM
        Infinity Fabric = PCIeIreland2017/03/15 04:49 PM
        Infinity Fabric = PCIeRicardo B2017/03/15 10:25 PM
        Infinity Fabric = PCIeslacker2017/03/15 10:45 PM
          Infinity Fabric = PCIeRicardo B2017/03/15 11:02 PM
            Infinity Fabric = PCIeAaron Spink2017/03/16 01:08 AM
              Infinity Fabric = PCIeRicardo B2017/03/16 05:30 AM
                Infinity Fabric = PCIeAaron Spink2017/03/16 10:58 AM
        Infinity Fabric = PCIeGabriele Svelto2017/03/16 03:48 AM
          Latency vs. bandwidthDavid Kanter2017/03/16 08:04 AM
      Infinity Fabric = PCIeGroo2017/03/15 05:35 PM
        Infinity Fabric = PCIeslacker2017/03/15 11:11 PM
          Infinity Fabric = PCIeAdrian2017/03/16 02:51 AM
            Infinity Fabric = PCIeMichael S2017/03/16 04:32 AM
              Infinity Fabric = PCIeAdrian2017/03/16 07:58 AM
                Infinity Fabric = PCIeRicardo B2017/03/16 09:16 AM
                  Infinity Fabric = PCIeMichael S2017/03/16 09:54 AM
                    Infinity Fabric = PCIeRicardo B2017/03/16 10:07 AM
                      Infinity Fabric = PCIeMichael S2017/03/16 02:33 PM
                        Infinity Fabric = PCIeGabriele Svelto2017/03/17 03:35 AM
                          Infinity Fabric = PCIeAaron Spink2017/03/17 10:25 AM
                            Thanks, your posts on this thread have been extremely informative (NT)Gabriele Svelto2017/03/17 01:08 PM
                            Infinity Fabric = PCIeRicardo B2017/03/17 06:08 PM
                              Infinity Fabric = PCIeAaron Spink2017/03/17 06:27 PM
                              Quickpath papers - circuits and implementationslacker2017/03/18 06:50 PM
                                Quickpath papers - circuits and implementationRicardo B2017/03/19 08:07 AM
                    Infinity Fabric = PCIeAaron Spink2017/03/16 11:11 AM
                      Infinity Fabric = PCIeMichael S2017/03/16 02:46 PM
                        Infinity Fabric = PCIeRicardo B2017/03/16 03:07 PM
                          Infinity Fabric = PCIeMichael S2017/03/16 05:13 PM
                            Infinity Fabric = PCIeAaron Spink2017/03/16 11:04 PM
                            Infinity Fabric = PCIeRicardo B2017/03/16 11:30 PM
                              Infinity Fabric = PCIeMichael S2017/03/17 07:24 AM
                                Infinity Fabric = PCIeRicardo B2017/03/17 06:07 PM
              Infinity Fabric = PCIeDavid Kanter2017/03/16 08:36 AM
                Infinity Fabric = PCIeMichael S2017/03/16 08:50 AM
                  Infinity Fabric = PCIeAaron Spink2017/03/16 11:24 AM
                    Infinity Fabric = PCIeMichael S2017/03/16 02:45 PM
                      Infinity Fabric = PCIeAaron Spink2017/03/16 11:21 PM
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