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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ajlueke - Tuesday, September 17, 2019 - link
More specifically, I was referring to this test from the article."Because of the new binning strategy – and despite what some of AMD's poorly executed marketing material has been saying – PBO hasn't been having the same effect, and users are seeing little-to-no benefit. This isn’t because PBO is failing, it’s because the CPU out of the box is already near its peak limits, and AMD’s metrics from manufacturing state that the CPU has a lifespan that AMD is happy with despite being near silicon limits."
What silicon limits exactly? AMDs marketing material has always indicated that a CPU will boost until it reaches either the PPT, TDC, EDC, or thermal limits. If none of those are met, it will boost until Fmax, which it simply will not exceed. Now, in a single threaded workload, the user is almost never at a PPT,TDC, EDC or thermal limit, and seem to be just shy of Fmax anyway. Now, if the user enables the auto-oc feature and extends Fmax by 100, 150 or 200MHz...nothing happens. The identical clockspeed and performance are observed.
I see the same thing happen in multicore on my 3900X. I normally hits the EDC and PPT limits under standard boosting. If I remove them, with precision boost overdrive, it does boost higher, but not by much. It again seems to stop a certain point. Again, EDC, TDC and PPT motherboard limits are not met, I am certainly not at Fmax, and the chip is under 70C, but it stops nonetheless. Nothing I can do makes it boost further.
"The Stilt", seems to mention the silicon fitness monitoring feature (FIT) in his "Matisse Strictly Technical" post on overclock.net. FIT appears to be a specific voltage limit for high and low current the CPU cannot exceed. This has never been included in AMDs documentation, and would help explain why the processor's stop boosting when according to AMD's own documentation, they should keep on going. So what exactly is this feature, and how does it work? I think that answer would do a great deal to alleviate user confusion.
mabellon - Tuesday, September 17, 2019 - link
>> "To a certain extent, Intel already kind of does this with its Turbo Boost Max 3.0 processors... [the] difference between the two companies is that AMD has essentially applied this idea chip-wide and through its product stack, while Intel has not, potentially leaving out-of-the-box performance on the table."What does this mean? What has Intel not done that AMD has done? Both have variable max frequency per core. Both expose this concept to the OS. Both rely on the same Window scheduler. What are you alluding to is different here?
It seems to me that Intel's HEDT platform with Turbo 3.0 is very much similar to AMD's implementation in the sense of having certain cores run faster. @Ian how is performance left on the table for Intel here? (Intel non HEDT is obviously stuck on Turbo 2.0 which is at a disadvantage)
Targon - Tuesday, September 17, 2019 - link
The majority of Intel chips are multiplier locked, so there isn't any real overclocking ability to speak of. It is only the k chips that users can overclock. AMD on the other hand, has PBO which is more advanced when it comes down to it.edzieba - Thursday, September 19, 2019 - link
"What does this mean? What has Intel not done that AMD has done?"Intel picks the maximum 'turbo' bin as the lowest that any core can achieve. AMD picks their maximum boost bin as the highest that any single core could achieve. 'Turbo 3.0' pre-selected two cores that were able to clock above the all-core turbo bin and allowed them to clock higher for lightly threaded workloads.
Jaxidian - Tuesday, September 17, 2019 - link
Is this WSL tool available for us to use? I'd love to have a better view of what speeds my cores could hit with a tool like this. In fact, I'd probably use it to map out all 12 cores (disabling 11 of them at a time). Obviously even that wouldn't quite give the whole picture, but it would be an interesting baseline map to have for my 3900x chip.Jaxidian - Tuesday, September 17, 2019 - link
I got my "no" answer here: https://twitter.com/IanCutress/status/117401405985..."It's a custom kludgy thing for internal use."
MFinn3333 - Tuesday, September 17, 2019 - link
I miss the old days when I would just push the Turbo frequency on my 286 and the CPU would go from 10MHz to 12MHz. Sure occassionally chip poppped off from the Glue but it was totally worth it to play Dune 2.sing_electric - Tuesday, September 17, 2019 - link
"Turbo, in this instance, is aspirational. We typically talk about things like ‘a 4.4 GHz Turbo frequency’, when technically we should be stating ‘up to 4.4 GHz Turbo frequency’."This is true, but EXACTLY the problem. The marketing teams at AMD, Intel and everyone else KNOW that when you see "3.6 GHz / 4.5 GHZ Turbo" written on a box, your eye falls to the second, larger number, and that's what sticks in your head.
Why should the consumer know that some of the numbers on the box (core count, base freq) are guaranteed, but some (turbo) aren't? That makes no sense and is borderline deceptive. And this doesn't just matter to the fairly small, tech savvy group of people who buy a processor alone in a box - here's how Dell lists the processor on its base config XPS 13 laptop when you go to "Tech Specs & Customization"
"8th Generation Intel® Core™ i5-8265U Processor (6M Cache, up to 3.9 GHz, 4 cores)"
Dell doesn't even bother LISTING the base frequency, even when you click to get more detail - how's a consumer supposed to gauge how fast their processor is? (To their credit, Apple, HP and Lenovo all list base frequency and "up to" the turbo).
Turbo is a great technology for getting the most out of limited silicon, but both AMD and Intel are, while not QUITE being untruthful, certainly trying to put their products in as good of a light as possible.
DigitalFreak - Tuesday, September 17, 2019 - link
That's marketing for you. Step as close to the "deceive the customer" line as possible without getting sued.Jaxidian - Tuesday, September 17, 2019 - link
I'm looking at the retail box for my 3900x right now. The only thing it says about frequencies is "4.6 GHz Max Boost, 3.8 GHz Base". There is no "up to" verbiage anywhere on the box. From a FTC advertising standpoint, the 4.6GHz should be guaranteed even if only under nuanced "limited single-core" and "with specific but reasonable motherboard, cooling, and software" scenarios.While this is a very good article and I generally have very few issues with AMD's new approach here, I'm of the belief that legally, a 3900x should be guaranteed to hit 4.6GHz when in a specific-yet-real-world scenario. I don't mean $100 mobos with $25 coolers should be able to hit it. But a better-than-budget x570 motherboard using the stock cooler with proper updates on a supported OS should absolutely hit 4.6GHz with certain loads. Otherwise, I think there's a real legal issue here.
All this said, I am now seeing 4.6GHz from time to time on my 3900x with ABBA on my x570 Aorus Master, so we're good here. Never saw higher than 4.575 before ABBA.