New Zen microarchitecture details

Discussion in 'CPUs and Overclocking' started by Dresdenboy, Mar 1, 2016.

  1. Doom2pro

    Doom2pro Senior member

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    So transistors that leak more (I assume you mean Drain-Source leakage) in cutoff state have a lower threshold voltage (Saturation voltage).

    Is that unique to FinFETs or is that true for all MOSFETs? I always assumed MOSFETs with a lower threshold voltage had lower RDS(on) as well as lower DS leakage.
     
    #2076 Doom2pro, Jun 29, 2016
    Last edited: Jun 29, 2016
  2. KTE

    KTE Senior member

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    ^Vth is beside the point here.

    Higher leakage chips require lower voltage to fit within the TDPs. It's one way we can spot them, and what The Stilt is talking about. It's been this trend for at least 15 years now.

    Sent from HTC 10
    (Opinions are own)
     
  3. The Stilt

    The Stilt Golden Member

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    Lower voltage is only better if the actual power / current draw is also lower. And in case of high leaking semiconductors they never are.

    Higher leakage ASICs require lower voltage to operate and generally have significantly better voltage scaling than ASICs with lower leakage characteristics. The trouble is that since they consume the same or even slightly higher amounts of power as the ASICs with low leakage characteristics, the currents will be higher. The higher currents cause temperature rise not just within the ASIC itself but throught the entire system. Higher current draw will stress the power delivery further and increase the power consumption by resulting in a lower conversion efficiency and in higher conduction losses. On ASICs with lower leakage characteristics it is completely the other way around. They require higher voltages to operate, but draw significatly lower amounts of current and therefore run significantly cooler.

    A ASIC with high leakage characteristcs is only desireable when you have basically an infinite amount of cooling (i.e phase change, LN2) and power delivery capacity available and the ASIC in question has a certain Vmax you need to work with. Usually the absolute voltage is relatively similar between the highest and the lowest leaking ASICs. Due their worse voltage scaling, the lower leaking ASICs might actually run into the Vmax barrier before reaching their Fmax.

    For the normal consumers only products with low or average leakage characteristics are desireable, as it provides the best overall system efficiency and the lowest temperatures.
     
  4. Abwx

    Abwx Diamond Member

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    That s a general rule for fets/mosfets, RDSon is dependent of the device conductance, if the device conduct more when switched off it will also conduct more (lower RDSon) when switched on.

    For a given operating voltage current through the device will rise quasi exponentialy as long as the gate voltage is below threshold, this latter level is the one at wich the exponential evolution has converged to a square law evolution (drain/source current in function of gate voltage).
     
  5. itsmydamnation

    itsmydamnation Golden Member

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  6. behrouz

    behrouz Senior member

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    If I'm not mistaken.
    1) Higher leakage ASICs = If Voltage = 1v then 10amp needs to match 10w.
    2) Lower leakage ASICs = If Voltage = 2v then 5 amp needs to match 10w.

    Muropaketti had RX40 with 87.1% Asic , So this means Card was running at low voltage with very high amp = High Temp = throttle at stock

    Right?
     
  7. The Stilt

    The Stilt Golden Member

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    Roughly so.
     
  8. Dresdenboy

    Dresdenboy Golden Member

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    I'm no MsEE, but I thought about the new AVFS of Polaris, which seems to be rather similar to CZ/BR's.
    THG created this nice chart of the power consumption, which seems to have heavy peaks:
    [​IMG]
    Source

    They used HZO55 power probes, which work up to 100 kHz:
    https://cdn.rohde-schwarz.com/pws/d...anuals/gb_1/h/hzo/HAMEG_MAN_D_E_F_S_HZO50.pdf
    Frequency range: DC to 100kHz (0.5dB)
    di / dt response: 20A/μs

    For voltage they used HZ355 500MHz probes.

    Now I wonder if a delay, phase shift, sampling resolution, etc. of these different ways to measure currents and voltages is good enough to catch the fast switching of Polaris' AVFS.

    So my first question is: How fast are these changes in V and F?
    Here is some SVI2 related documentation for AMD APUs: http://www.intersil.com/content/dam/Intersil/documents/isl9/isl95712.pdf

    Second question: Does this and the way of measuring separate values lead to errors when combining them to get the power?

    One idea is to verify the measurement setup by measuring wall power at constant GPU load with a card having slow V/F transitions and repeat that with the RX480.

    Albeit it's off topic, I think we have the right experts residing in this very thread. ;)
     
    #2083 Dresdenboy, Jun 30, 2016
    Last edited: Jun 30, 2016
  9. The Stilt

    The Stilt Golden Member

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    The AVFS reaction time is extremely fast (claimed to be < 1ns), however practically the speed of the intervention is limited by the VRM itself. AMD uses top notch digital "Comanche" (IR3567) VRM controller on these cards and the controller can adjust the output voltage at rate of no more than 25mV per 1µs. The actual speed will vary depending on the structure and the configuration of the VRM thou.

    If Polaris actually has AVFS enabled I think it is the first AMD product actually using it. AMD has had some fancy stuff in the GPU since Tonga (such as clock stretcher), however neither Tonga or Fiji used it (disabled all the time). Also Carrizo which was the first design to implement AVFS didn't have it enabled, or at least I have never seen it activating, during the ~ year of use.
     
  10. maddie

    maddie Golden Member

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    I posted this in the RX480 thread and got no response. You guys here might make some sense of this and offer an explanation. I consider it relevant for the upcoming Zen as this tech will almost certainly be used in it.

     
  11. el etro

    el etro Golden Member

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    ^ Great variation of consumption. Getting the ASIC of all of their cards will help better to understand what's going on. Adored TV and bitsandchips get power consumption under of what R380 consumes by some ~20W, which puts the consumption at a very acceptable range. And BTW computerbase and techpowerup reported their samples don't perform at 1266Mhz all the time, computerbase reports is because the RX card limits the power consumption before reach certain power level. All their cards perform closely.

    Maybe powertune is just doing his work and power consumption varies from one card to another?
     
  12. NostaSeronx

    NostaSeronx Golden Member

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    Boop. Not specifically Carrizo, but specifically with Excavator. So, Polaris is the second design to implement AVFS.
    [​IMG]
    ((Guys, it says excavator core not excavator module!)) [Triggered]

    Each orange blob helps with;
     
    #2087 NostaSeronx, Jun 30, 2016
    Last edited: Jun 30, 2016
  13. Abwx

    Abwx Diamond Member

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    No, because detection of a voltage drop and voltage correction of this drop
    are two different things, the former can be extremely fast while the latter is dependent of the supply switching frequency, for instance a voltage drop can be measured within 10MHz bandwith but if the supply switching frequency is 100KHz then it will require a few 10us cycles to correct the voltage value.

    The principle of AMD s AVFS is to reduce frequency accordingly during the voltage drop rather than trying to correct the voltage as there would be an inherent voltage spike that is of the same value as the drop, hence this would be less efficient power wise.
     
    #2088 Abwx, Jun 30, 2016
    Last edited: Jun 30, 2016
  14. Ajay

    Ajay Diamond Member

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  15. NostaSeronx

    NostaSeronx Golden Member

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    That is Steamroller, Adaptive Clocking.

    AVFS is best known for its per device voltage calculation;
    https://i.imgur.com/niOuEKC.jpg
    - Bullet Pt 4 -> Smarter System will adapt operating voltage per device.

    Bristol Ridge;
    http://i.imgur.com/P4vSuBt.png
    http://i.imgur.com/lsfF0Zq.png
     
    #2090 NostaSeronx, Jun 30, 2016
    Last edited: Jun 30, 2016
  16. CHADBOGA

    CHADBOGA Golden Member

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    When we will get some good performance info?
     
  17. Phynaz

    Phynaz Diamond Member

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    Considering how quiet AMD was about Polaris and how that turned out, the silence about Zen doesn't fortell good things.

    Of course I've been saying that for a while, so we'll see if I'm correct.
     
  18. Abwx

    Abwx Diamond Member

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    What you linked is something else, it s a dynamic compensation of the transistors static parameters, these are variables with a dependency on waffers quality (wich will yield devices with dispersion in conductance and threshold voltage), operating temperature and voltage.
     
  19. Ajay

    Ajay Diamond Member

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    Having seen Polaris 10, it seems critical for Zen to come out as late as possible. Not only does the process variability need to be reduced but yields at higher clocks probably needs a significant boost. I wish we had more visibility into GloFlo's 14LPP process. I also sincerely wish Zen was designed using a better process.
     
  20. DrMrLordX

    DrMrLordX Diamond Member

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    Wait, what "process variability"? We're jumping to a lot of conclusions here, no? I have had Hawaii cards develop horrible current leakage problems (which can be addressed somewhat via BIOS modding) during usage, particularly after extended periods of high heat/100% utilization in compute tasks(mining). The GPU quality didn't spontaneously shift during usage, and rather it seems that the VRMs go bad (or partially bad).

    Hasn't anyone investigated the possibility that some of the review cards have wonky VRMs?
     
  21. Abwx

    Abwx Diamond Member

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    Dispersion of the transistors characteristics from a waffer to another and even within a same waffer, finfets have significantly more dispersion than planar transistors, whatever the manufacturer..
     
  22. Ajay

    Ajay Diamond Member

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    VRM problems could be at work here, but that's a different issue. The variation is ASIC quality, as Abwx just noted - is even more a problem w/FinFets and is an issue also pointed out by others above. There are additional hints that GF is having problems with it's 14LPP process node. No particulars - hence my complaint about the lack of visibility in exactly what is going on at GF (if we still have industry insiders here, they are not talking) - so I certainly could be wrong about the state of 14LPP.

    The problem AMD faces, is that it has much to prove. AMD's FAB, Global Foundries, doesn't have a great record of pulling through for them in a timely manner.
     
  23. Elixer

    Elixer Diamond Member

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    There are just too many unknowns at work here.
    We are all trying to guess why GloFlo's 14nm LPP is subpar to what should have been a much lower power design.
    Yes, something is wrong, could be die size + 14nm LPP, could be material, could be faulty design by AMD, could be the 14nm process itself, and on and on. We just don't know.

    At this point, looking at the 480, it seems Zen will be lower speeds, and higher temps and nobody wants that, we need strong competition.

    AMD won't say anything yet, we need to wait for the 'quiet period' to expire to get a glimpse of what is going on.
     
  24. itsmydamnation

    itsmydamnation Golden Member

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    They already did comment on it and i posted a damn link in this thread like a day ago........
     
  25. The Stilt

    The Stilt Golden Member

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    This time you are absolute correct :D

    I must admit that I'm not too familiar with AVFS.

    If AVFS operation requires releasing and re-engaging the Pll locking (which I expect it does), I would say the minimum delay for AVFS operation is actually around 2µs. That's the Pll lock time on Excavator (200 x 10ns) designs and Polaris appears to be using almost identical PM.