Reaching for Turbo: Aligning Perception with AMD’s Frequency Metrics
by Dr. Ian Cutress on September 17, 2019 10:00 AM ESTA Short Detour on Mobile CPUs
For our readers that focus purely on the desktop space, I want to dive a bit into what happens with mobile SoCs and how turbo comes into effect there.
Most Arm based SoCs use a mechanism called EAS (Energy-Aware Scheduling) to manage how it implements both turbo but also which cores are active within a mobile CPU. A mobile CPU has one other aspect to deal with: not all cores are the same. A mobile CPU has both low power/low performance cores, and high power/high performance cores. Ideally the cores should have a crossover point where it makes sense to move the workload onto the big cores and spend more power to get them done faster. A workload in this instance will often start on the smaller low performance cores until it hits a utilization threshold and then be moved onto a large core, should one be available.
For example, here's Samsung's Exynos 9820, which has three types of cores: A55, A75, and M4. Each core is configured to a different performance/power window, with some overlap.
Peak Turbo on these CPUs is defined in the same way as Intel does on its desktop processors, but without the Turbo tables. Both the small CPUs and the big CPUs will have defined idle and maximum frequencies, but they will conform to a chip-to-chip defined voltage/frequency curve with points along that curve. When the utilization of a big core is high, the system will react and offer it the highest voltage/frequency up that curve as is possible. This means that the strongest workloads get the strongest frequency.
However, in Energy Aware Scheduling, because the devices that these chips go into are small and often have thermal limitations, the power can be limited by battery or thermals. There is no point for the chip to stay at maximum frequency only to burn in the hand. So the system will apply an Energy Aware algorithm, combined with the thermal probes inside the device, to ensure that the turbo and workload tend towards a peak skin temperature of the device (assuming a consistent, heavy workload). This power is balanced across the CPU, the GPU, and any additional accelerators within the system, and the proportion of that balance can be configured by the device manufacturer to respond to what proportion of CPU/GPU/NPU instructions are being fed to the chip.
As a result, when we see a mobile processor that advertises ‘2.96 GHz’, it will likely hit that frequency but the design of the device (and the binning of the chip) will determine how long before thermal limits kick in.
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allenb - Tuesday, September 17, 2019 - link
Nicely done, Ian, very nicely done. The PC hardware world could do with more reporting like this.eva02langley - Wednesday, September 18, 2019 - link
Indeed, all the so called PC tech press should be ashamed of how they spun this story. Toms didn`t even switch motherboard while testing this issue. The motherboard was the problem and they just transposed the problem to all their testings.Toms is officially a joke of a site. Nothing coming from them since Just Buy It! can be trusted.
JasonMZW20 - Tuesday, September 17, 2019 - link
As always, very insightful background, analysis, and ultimate conclusions, Dr. Cutress (had to shoe that in because it sounds cool, right?).I felt it was a bit overblown and I knew that performance with the "fixed" BIOS would be within standard deviation. I said as much on Reddit too. Software polling has limitations, as you rightly pointed out.
Arbie - Tuesday, September 17, 2019 - link
A very high quality article - upholding the AT standard for sure - which was sorely needed. Thanks!davide445 - Wednesday, September 18, 2019 - link
Finally an intelligent article looking at objective elements.So bored in reading Tom's hardware articles (that I avoid as possible if there are any other option) , where is clear in my opinion the focus as pro Intel ads. Fast articles so they are the only one on the subject, no real deepening of the subject but only on controversial elements, no comments possible so just a single opinion. Unfortunately I suppose this is how media is working and getting paid.
Peter2k - Wednesday, September 18, 2019 - link
Just a note that der8auer actually asked AMD, and AMD told him, which software to use, which frequency for monitoring and which software to use to produce loadWhich Windows version, which drivers,....
So how to monitor and how its read, sure, but AMD did specify, so by AMD rules it should stack up to AMD marketing figures
Secondly
Ryzen 3000 is a good CPU even when missing 50Mhz, if they can't boost that, then don't advertise on the "optimistic side"
If silicone lottery really plays into this, just be pragmatic about it
Thirdly
Don't have an official marketing video out talking, and drawing curves, about reaching 4.75 when most CPU's can't really reach 4.5
eva02langley - Wednesday, September 18, 2019 - link
Well, some of the chips are hitting the announced frequency...And now even more after this new AGESA update.
Oliseo - Wednesday, September 18, 2019 - link
Dude, asking a bunch of techies who follow sites like this and deciding that 67% of customers do not expect CPU's to hit their turbo frequencies... Do I need to state the obvious here?If the average Joe see's "4.7Ghz Turbo", they expect "4.7 Turbo", and anything else than that is fraud.
eva02langley - Wednesday, September 18, 2019 - link
You read the article? Those are not guaranteed speed and most of the time the difference in speed doesn`t translate in better performances.twtech - Thursday, September 19, 2019 - link
Yes, I read the article, I read and understood the reasoning behind it - I still disagree with it. If most of your chips can only hit 4.5 and not 4.7, then market it as 4.5 GHz turbo. If you want to sell the 4.7 chips as 4.7, then bin for it.