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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StrangerGuy - Wednesday, September 18, 2019 - link
Pretty much the only people left OCing CPUs are epeen wavers with more money than sense."$300 mobo and 360mm AIO for that Intel 8 core <10% OC at >200W...Look at all that *free* performance! Amirite?"
Korguz - Wednesday, September 18, 2019 - link
" Pretty much the only people left OCing CPUs are epeen wavers with more money than sense" that a pretty bold statement. i know quite a few people who overclock their cpus, because intel charged too much for the higher end ones, so they had to get a lower tier chip. with zen, thats not the case as much any more as they have switched over to amd, because by this time, they would of had to get a new mobo any way, because intels upgrade paths are only 2, maybe 3 years if they are lucky.dont " need " and AIO, as there are some pretty good air coolers out there, and some, dont like the idea of water, or liquid in their comps :-)
Xyler94 - Thursday, September 19, 2019 - link
Sorry, here's where I'll have to disagree with you.You'll never overclock an i3 to i5/i7 levels. If my choices were between an overclocking i3, with a Z series board, or a locked i5 with an H series board, I'd choose the i5 in a heartbeat, as that's just generally better. Overclocking will never make up the lack of physical cores.
So I agree, mostly these days overclocking is reserved for A: People with e-peens, and B:, people who genuinely need 5ghz on a single core... which are fewer than those who can utilize the multi-threaded horsepower of Ryzen... so yeah,
evernessince - Tuesday, September 17, 2019 - link
Does it deliver well? I see plenty of people on the Intel reddit not hitting advertised turbo speeds. That's considering they are using $50+ CPU coolers as well."Pretty impressive to see a server cpu with 20% lower ST performance only because the
low power process utilized is unable to deliver a clock speed near 4Ghz, absurd thing considering
that Intel 14nm LP gives 4GHz at 1V without struggles."
What CPU are you talking about? Even AMD's 64 core monster has damn near the same IPC as the Intel Xeon 8280 (thanks to Zen 2 IPC improvements) and that CPU has LESS THEN HALF THE CORES and only consumes 20w more. The Intel CPU also costs almost twice as much. Only a moron brings up single threaded performance in a server chip conversation anyways, it's one of the least important metric for server chips. AMD's new EPYC chip crushes Intel in Core count, TCO, power consumption, and security. Everything that is important to server.
yankeeDDL - Wednesday, September 18, 2019 - link
You do realize that the clock speed does not depend only by the process, right? Your comment sounds like that that of a disgruntled Intel fanboy trying to put AMD in under a bar light. For 25MHz.Spunjji - Monday, September 23, 2019 - link
Absolute codswallop. AMD are getting 100-300Mhz more on their peak clock speeds for Zen2 with this first-gen 7nm process tech than they were seeing with Zen+ 12nm (and nearly 400Mhz more than Zen on 14nm), so nothing about that implies that 7nm is slower than 14nm. Intel's architecture and process tech are not remotely comparable to AMD's, and we don't know what is the primary limiting factor on Zen clockspeeds.Not sure why you're claiming lower ST performance on the server parts either - Rome is better in every single regard than its predecessors, and it's better pound-for-pound than anything Intel will be able to offer in the next 12-18 months.
PeachNCream - Tuesday, September 17, 2019 - link
I see a tempest in a teapot on the stove of a person who is busy splitting hairs at the kitchen table. It would be more interesting to calculate how much energy and time was expended on the issue to see if the performance uplift from the fix will offset the global societal cost of all the clamoring this generated. For that, I suppose you'd have to know how many Ryzen chips are actually doing something productive as opposed to crunching at video games.The idea of buying cheaper hardware for non-work needs sticks here. Less investment means less worry about maximizing your return on your super-happy-fun-box and less heartburn over a little bit of clockspeed on a component that plays second fiddle to GPU performance when it comes to entertainment anyway.
psychobriggsy - Tuesday, September 17, 2019 - link
Ultimately in the end it isn't MHz that counts, it is observed performance in the software that you care about. That's why we read reviews, and why the review industry is so large.If performance X was good enough, does it matter if it was achieved at 4.5GHz or 4.425GHz? Not really. But if the CPU manufacturer is using it as a primary competitive comparison metric (rather than a comparative metric with their other SKUs) then it has to be considered, like in this article.
It is sad that MHz is still a major metric in the industry, although now Intel IPC is similar to AMD IPC, it is actually kinda relevant.
What I'd like is better CPU power draw measurements versus what the manufacturer says. Because TDP advertising seems to be even more fraught with lies/marketing than MHz marketing! Obviously most users don't care about 10 or 20% extra power draw at a CPU level, as at a system level it will be a tiny change, but it's when it is 100% that it matters.
IMO, I'd like TDPs to be reported at all core sustained turbo, not base clocks. Sure, have a typical TDP measurement as well as the more information the better, but don't hide your 200W CPU under a 95W TDP.
TechnicallyLogic - Tuesday, September 17, 2019 - link
Personally, I feel that AMD should have 2 numbers for the max frequency of the CPU; "Boost Clock" and "Burst Clock". Assuming that you have adequete cooling and power delivery, the boost clock would be sustainable indefinitely on a single core, while the burst clock would be the peak frequency that a single core on the CPU can reach, even if it's just for a few ms.fatweeb - Tuesday, September 17, 2019 - link
I could see them eventually going in this direction considering Navi already has three clocks: Base, Gaming, and Boost. The first two would be guaranteed, the last not so much.