Saturday, March 4, 2017

Characterizing Ryzen R7 overlocking behavior

It's been a while since I made an overclocking post, mainly because nothing interesting has happened since Sandy Bridge. Ryzen has been the first new thing in half a decade to hit the market, so I dutifully went and bought a R7 1700 and an Asus PRIME B350-Plus in the name of science.

All tests were done using a 400W Antec server supply. CPU currents were measured using a clamp DC ammeter on the 12V wires going into the CPU 8-pin. The rest of the setup consisted of Windows 10 Enterprise (I made sure Defender and Windows Update were disabled), an XFX HD5750 for basic video output, and a 320GB 7200RPM 2.5" drive. Not the most upscale of setups, but unlikely to affect overclocking figures.Everything was done on an open-air setup in a room with ~20C ambient temperatures - I expect stock cooler mileage to go down slightly in a case with higher ambient temps. Adjustments were made on-the-fly in Ryzen Master.

Stock cooler numbers

Wraith Spire is remarkably good for a stock cooler, able to hold off 120W while remaining reasonably cool. Gone are the days of shitty stock coolers that would run stock-clocked i7's at 90C.

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The bad news: 3.8GHz seemed somewhat unattainable on the stock cooler; there was a distinct feeling of thermal runaway (Prime95 would run until temps hit about 76C or so and then crash, but not hard enough to bring down Windows).

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Power seems quite in check out to 3.7GHz, and is not great at 3.8GHz, though you do lose some efficiency past 3.5GHz.

High-End Air numbers
I broke out the old Thermalright TRUE 120 for some testing; it's not a modern cooler by any means but it could cool 200+W 45nm processors back in the day so I figured it would be fine. Note that numbers up to 37x are the stock cooler numbers from above, the stock cooler did a good enough job that I didn't bother rerunning the benchmarks.

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40x was pretty much unattainable on my setup. Temperatures climbed rapidly, eventually crashing hard enough to trigger a reboot. I'm pretty sure this is a die thermal resistance limit; it is just not possible to remove 25W per core on Ryzen's die while maintaining the sub-70C temps needed for stability. I tried 1.4375V as well, but power climbed to 204W (17A) and the system similarly rebooted.

4C/8T numbers
Going by the theory that the frequency wall at 39x was thermal, I disabled four cores in hopes that the lateral heat conduction in the die would reduce temperatures substantially.

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While temperatures did go down dramatically, enabling much improved operation at 40x, 41x was very out of reach; temperatures remained in control, but Windows crashed before I could get meaningful power readings.

Prime95 Blend numbers
Not satisfied with the lack of 4GHz, and still going by the thermal stability theory, I tried Blend, which I figured is more representative of enthusiast thermal loads.

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It pulled off 40x fine, albeit requiring slightly more voltage to do so than the quad core test (crash after about 10 minutes of blending at 1.375V) As a bonus, the lower temps also translate into slightly reduced voltage requirements.


Voltage/Power scaling
For science's sake, I left the multiplier at 30x and slowly raised the voltage.

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Not as interesting as I expected, looks like standard quadratic-ish scaling out to 1300mV, then something happens, resulting in a bump in power consumption. The bump is looks like part of the reason we can't get past 40x, if process refinements could move it out we'd get more

Conclusions

  • Ryzen Master is pretty good. After leaving it running for half an hour while I wrote up this post it crashed, but seemed to work fine when I reopened it. The UI is damn responsive for a overclocking tool, as good as any I've ever used.
  • The PRIME B350-Plus BIOS is not great as far as overclocking goes. In particular, the option to set a fixed voltage is missing, and I have no idea what the 'FID' and 'DID' ratios do (raising DID seems to lower the target frequency??). Presumably this will be remedied in a later BIOS release.
  • Ryzen, or at least my sample, seems to have poor frequency-temperature characteristics past about 75C. On both the 38x stock and 40x aftermarket tests, Windows crashed when the temperature readout in Ryzen Master crossed 75C.
  • It looks like on 8 cores, the thermal limitations come from the ability to pull heat out of the die, not because of the thermal resistance of the heatsink to air. Temperatures climbed rapidly in response to frequency changes, and at least qualitatively, the fins on the TRUE 120 were quite cold.
  • On 4 cores, efficiency is solid. Voltage scaling is not as good as Kaby Lake (which ships at 4.2GHz and typically in the 1.225V neighborhood), but power consumption is in control and temperatures are very low.
  • Ryzen has two distinct bumps in efficiency. I'm wary of saying where they are based on a single sample, but it looks like the first is in the neighborhood of 35x and the second, around 38x. Pushing for that last two bins (or eight, if you want to be picky) causes an insane increase in power consumption on my sample; the sample to sample cutoff may vary but I feel safe in saying that you will lose a whole lot of performance/watt right around 3.8+/- GHz.

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