Defining Turbo, Intel Style

Since 2008, mainstream multi-core x86 processors have come to the market with this notion of ‘turbo’. Turbo allows the processor, where plausible and depending on the design rules, to increase its frequency beyond the number listed on the box. There are tradeoffs, such as Turbo may only work for a limited number of cores, or increased power consumption / decreased efficiency, but ultimately the original goal of Turbo is to offer increased throughput within specifications, and only for limited time periods. With Turbo, users could extract more performance within the physical limits of the silicon as sold.

In the beginning, Turbo was basic. When an operating system requested peak performance from a processor, it would increase the frequency and voltage along a curve within the processor power, current, and thermal limits, or until it hit some other limitation, such as a predefined Turbo frequency look-up table. As Turbo has become more sophisticated, other elements of the design come into play: sustained power, peak power, core count, loaded core count, instruction set, and a system designer’s ability to allow for increased power draw. One laudable goal here was to allow component manufacturers the ability to differentiate their product with better power delivery and tweaked firmwares to give higher performance.

For the last 10 years, we have lived with Intel’s definition of Turbo (or Turbo Boost 2.0, technically) as the defacto understanding of what Turbo is meant to mean. Under this scheme, a processor has a sustained power level, and peak power level, a power budget, and assuming budget is available, the processor will go to a Turbo frequency based on what instructions are being run and how many cores are active. That Turbo frequency is governed by a Turbo table.

The Turbo We All Understand: Intel Turbo

So, for example. I have a hypothetical processor that has a sustained power level (PL1) of 100W. The peak power level (PL2) is 150W*. The budget for this turbo (Tau) is 20 seconds, or the equivalent of 1000 joules of energy (20*(150-100)), which is replenished at a rate of 50 joules per second. This quad core CPU has a base frequency of 3.0 GHz, but offers a single core turbo of 4.0 GHz, and 2-core to 4-core of 3.5 GHz.

So tabulated, our hypothetical processor gets these values:

Sustained Power Level PL1 / TDP 100 W
Peak Power Level PL2 150 W
Turbo Window* Tau 20 s
Total Power Budget* (150-100) * 20 1000 J
*Turbo Window (and Total Power Budget) is typically defined for a given workload complexity, where 100% is a total power virus. Normally this value is around 95%

*Intel provides ‘suggested’ PL2 values and ‘suggested’ Tau values to motherboard manufacturers. But ultimately these can be changed by the manufacturers – Intel allows their partners to adjust these values without breaking warranty. Intel believes that its manufacturing partners can differentiate their systems with power delivery and other features to allow a fully configurable value of PL2 and Tau. Intel sometimes works with its partners to find the best values. But the take away message about PL2 and Tau is that they are system dependent. You can read more about this in our interview with Intel’s Guy Therien.

Now please note that a workload, even a single thread workload, can be ‘light’ or it can be ‘heavy’. If I created a piece of software that was a never ending while(true) loop with no operations, then the workload would be ‘light’ on the core and not stressing all the parts of the core. A heavy workload might involve trigonometric functions, or some level of instruction-level parallelism that causes more of the core to run at the same time. A ‘heavy’ workload therefore draws more power, even though it is still contained with a single thread.

If I run a light workload that requires a single thread, it will start the processor at 4.0 GHz. If the power of that single thread is below 100W, then I will use none of my budget, as it is refilled immediately. If I then switch to a heavy workload, and the core now consumes 110W, then my 1000 joules of turbo budget would decrease by 10 joules every second. In effect, I would get 100 seconds of turbo on this workload, and when the budget is depleted, the sustained power level (PL1) would kick in and reduce the frequency to ensure that the consumption on the chip stayed at 100W. My budget of energy for turbo would not increase, because the 100 joules/second that is being added is immediately taken away by the heavy workload. This frequency may not be the 3.0 GHz base frequency – it depends on the voltage/power characteristics of the individual chip. That 3.0 GHz base value is the value that Intel guarantees on its hardware – so every one of this hypothetical processor will be a minimum of 3.0 GHz at 100W on a sustained workload.

To clarify, Intel does not guarantee any turbo speed that is part of the specification sheet.

Now with a multithreaded workload, the same thing occurs, but you are more likely to hit both the peak power level (PL2) of 150W, and the 1000 joules of budget will disappear in the 20 seconds listed in the firmware. If the chip, with a 4-core heavy workload, hits the 150W value, the frequency will be decreased to maintain 150W – so as a result we may end up with less than the ‘3.5 GHz’ four-core turbo that was listed on the box, despite being in turbo.

So when a workload is what we call ‘bursty’, with periods of heavy and light work, the turbo budget may be refilled quicker than it is used in light workloads, allowing for more turbo when the workload gets heavy again. This makes it important when benchmarking software one after another – the first run will always have the full turbo budget, but if subsequent runs do not allow the budget to refill, it may get less turbo.

As stated, that turbo power level (PL2) and power budget time (Tau) are configurable by the motherboard manufacturer. We see that on enterprise motherboards, companies often stick to Intel’s recommended settings, but with consumer overclocking motherboards, the turbo power might be 2x-5x higher, and the power budget time might be essentially infinite, allowing for turbo to remain. The manufacturer can do this if they can guarantee that the power delivery to the processor, and the thermal solution, are suitable.

(It should be noted that Intel actually uses a weighted algorithm for its budget calculations, rather than the simplistic view I’ve given here. That means that the data from 2 seconds ago is weighted more than the data from 10 seconds ago when determining how much power budget is left. However, when the power budget time is essentially infinite, as how most consumer motherboards are set today, it doesn’t particularly matter either way given that the CPUs will turbo all the time.)

Ultimately, Intel uses what are called ‘Turbo Tables’ to govern the peak frequency for any given number of cores that are loaded. These tables assume that the processor is under the PL2 value, and there is turbo budget available. For example, here are Intel’s turbo tables for Intel’s 8th Generation Coffee Lake desktop CPUs.

So Intel provides the sustained power level (PL1, or TDP), the Base frequency (3.70 GHz for the Core i7-8700K), and a range of turbo frequencies based on the core loading, assuming the motherboard manufacturer set PL2 isn’t hit and power budget is available.

The Effect of Intel’s Turbo Regime, and Intel’s Binning

At the time, Intel did a good job in conveying its turbo strategy to the press. It helped that staying on quad-core processors for several generations meant that the actual turbo power consumption of these quad-core chips was actually lower than sustained power value, and so we had a false sense of security that turbo could go on forever. With the benefit of hindsight, the nuances relating to turbo power limits and power budgets were obfuscated, and people ultimately didn’t care on the desktop – all the turbo for all the time was an easy concept to understand.

One other key metric that perhaps went under the radar is how Intel was able to apply its turbo frequencies to the CPU.

For any given CPU, any core within that design could hit the top turbo. It allowed for threads to be loaded onto whatever core was necessary, without the need to micromanage the best thread positioning for the best performance. If Intel stated that the single core turbo frequency was 4.6 GHz, then any core could go up to 4.6 GHz, even if each individual core could go beyond that.

For example, here’s a theoretical six-core Core i5-9600K, with a 3.7 GHz base frequency, and a 4.6 GHz turbo frequency. The higher numbers represent theoretical maximums of each core at the turbo voltage.

This is actually a strategy related to how Intel segments its CPUs after manufacturing, a process called binning. If a processor has the right power/thermal characteristics to reach a given frequency in a given power, then it could be labelled as the most appropriate CPU for retail and sold as such. Because Intel aimed for a homogeneous monolithic design, every core in the design was tested such that it performed equally (or almost equally) with every other core. Invariably some cores will perform better than others, if tweaked to the limits, but under Intel’s regime, it helped Intel to spread the workloads around as to not create thermal hotspots on the processor, and also level out any wear and tear that might be caused over the lifetime of the product. It also meant that in a hypervisor, every virtual machine could experience the same peak frequencies, regardless of the cores they used.

With binning, Intel (or any other company), is selecting a set of voltages and frequencies for a processor to which it is guaranteed. From the manufacturing, Intel (or others) can see the predicted lifespan of a given processor for a range of frequencies and voltages, and the ones that hit the right mark (based on internal requirements) means that a silicon chip ends up as a certain CPU. For example, if a piece of silicon does hit 9900K voltages and frequencies, but the lifespan rating of that piece of silicon is only two years, Intel might knock it down to a 9700K, which gives a predicted lifespan of fifteen years. It’s that sort of thing that determines how high a chip can perform. Obviously chips that can achieve high targets can also be reclassified as slower parts based on inventory levels or demand.

This is how the general public, the enthusiasts, and even the journalists and reviewers covering the market, have viewed Turbo for a long time. It’s a well-known part of the desktop space and to a large extent is easy to understand. If someone said ‘Turbo’ frequency, everyone was agreed on the same basic principles and no explanation was needed. We all assumed that when Turbo was mentioned, this is what they meant, and this is what it would mean for eternity.

Now insert AMD, March 2017, with its new Zen core microarchitecture. Everyone assumed Turbo would work in exactly the same way. It does not.

Reaching for Turbo: Aligning Perception with AMD’s Frequency Metrics AMD’s Turbo: Something Different
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  • GeoffreyA - Wednesday, September 18, 2019 - link

    Excellent article and detective work, Ian! Thank you for it. Also reminds me of observation in QM, where experiment affects the results. Anyway, have a great day.
  • eva02langley - Wednesday, September 18, 2019 - link

    "However, given recent articles by some press, as well as some excellent write-ups by Paul Alcorn over at Tom’s Hardware* "

    Please, I know you are parent sites, but HELL with that. Paul literally test the hardware with the SAME motherboard, the MSI GODLIKE x570 and never... ever mentioned anything close to a BIOS issue. He did an half-ass job that I could call as amateurish at best.

    In the meantime, Steve from HardwareUnboxed tested the same CPU on DIFFERENT board and concluded into BIOS immaturity, what I called on the first instance of Toms series of bashing article.
  • ajlueke - Thursday, September 19, 2019 - link

    I wouldn't necessarily agree, but the spirit of the statement is on track. In Paul Alcorn's write-up he attempted to associate the missing boost MHz, to a statement Shamino made about reliability, and then changes in thermal thresholds observed by "The Stilt".
    He never bothers to explain, why single threaded boosting (the thing everyone is complaining about) would be related to a threshold change from 80C to 75C when those temperatures are never observed during a lightly threaded workload. He then heats the boards up to those temps and looks at boosting, and sure enough, something changed just like the Stilt said. But what, if anything, does that have to do with the missing single thread boost MHz, when temps are well below 75C for most end users?
  • eva02langley - Wednesday, September 18, 2019 - link

    " 1. Popular YouTuber der8aur performed a public poll of frequency reporting that had AMD in a very bad light, with some users over 200 MHz down on turbo frequency,
    2. The company settled for $12.1m in a lawsuit about marketing Bulldozer CPUs,
    3. Intel made some seriously scathing remarks about AMD performance at a trade show,
    4. AMD’s Enterprise marketing being comically unaware of how its materials would be interpreted."

    And in the meantime in the same week...


    Like I told AdoredTV... we have a very different definition of BAD WEEK. Honestly, those issue are hiccup of any new platform launch.
  • eva02langley - Wednesday, September 18, 2019 - link

    "Others we ignored, such as (4) for a failure to see anything other than an honest mistake given how we know the individuals behind the issues, or the fact that we didn’t report on (3) because it just wasn’t worth drawing attention to it."

    The reason why you guys are pros. You didn`t do Intel dirty work for propagating their propaganda... unlike TomsHardware...
  • quadibloc - Wednesday, September 18, 2019 - link

    Both Intel and AMD should start marketing their chips as "an X GHz chip", where X is the base frequency, if the turbo frequency isn't a part of the basic specirication of the chip that it must meet. Since even at the base frequency, apparently AMD chips don't last forever, it looks like I'm going to be underclocking mine a little.
  • ballsystemlord - Wednesday, September 18, 2019 - link

    Spelling and grammar corrections:

    "Certain parts of how the increased performance were understood,..."
    Should be "was" not "were":
    "Certain parts of how the increased performance was understood,..."

    "...(standard is defined be Intel and AMD here, usually with a stock cooler, new paste, a clean chassis with active airflow of a minimum rate, and a given ambient temperature)..."
    "by" not "be":
    "...(standard is defined by Intel and AMD here, usually with a stock cooler, new paste, a clean chassis with active airflow of a minimum rate, and a given ambient temperature)..."

    "This ultimately would lead some believe that this relates to a thermal capacity issue within the motherboard, CPU, or power delivery."
    Missing "to":
    "This ultimately would lead some to believe that this relates to a thermal capacity issue within the motherboard, CPU, or power delivery."
  • Uroshima - Thursday, September 19, 2019 - link

    Very nice article.

    From what I understood, AMD has done tried to get as close to the limit of the silicon as possible regarding clocks. This allowed them to "survive" the transition to 7nm. Intel has kept a wide margin to the actual limits of the silicon and at 10nm (which is more or less 7nm of AMD) they struggle as the chips simply can't clock high enough.

    Could be, this is the reason Intel will stick with 14nm for high performance until new silicon comes out that is similar to the AMD "to the limits" approach? This would be roughly 3 years from when they decided this (Jim Keller's arrival?).

    I have a hunch that this is the future we are going towards, new nodes with diminishing returns (or even reductions) on clocks but advantages in power and number of transistors. Keeping close to the limit of the silicon will be the key for performance, right next to IPC.

    On the other hand I would even consider that for some applications, having a refined 14* nm process could be an advantage (up to a frankenmonster of a hybrid 7/14 with UV). Intel, with its vast resources, should definitely explore this option to not only follow the competition but maintain the low thread performance crown.

    But then, looks like AMD did their homework this time. :)
  • eva02langley - Thursday, September 19, 2019 - link

    You are bang on. Intel 10nm process cost more, is having low yield and the frequency drop over 14nm++ is not bringing meaningful performances for making the transition.

    This is why Intel is releasing new server, laptop and desktop CPUs on 14nm++. It cost less, having better yield and perform better.
  • eva02langley - Thursday, September 19, 2019 - link

    However the power consumption just cannot match TSMC 7nm.

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