Overclocking thermal velocity boost, or OCTVB, allows the user to manually configure the Thermal Velocity Boost behavior of Intel CPUs.
Intel OverClocking Thermal Velocity Boost (OCTVB)
Thermal Velocity Boost does two things.
- First, it decreases the operating voltage if the CPU temperature is below the TjMax.
- Two, it opportunistically increases the clock frequency above the Turbo Boost 2.0 and 3.0 frequencies if the CPU operates below a part-specific temperature threshold. This threshold is usually 70 degrees Celsius on desktop CPUs.
With the introduction of the Intel Cryo Cooling Technology in 2020, Intel opened up the TVB configuration to motherboard vendors. The feature is named OverClocking Thermal Velocity Boost, or OCTVB for short.
The easiest way to think of OCTVB is limiting, or clipping, the maximum allowed CPU ratio based on the CPU operating temperature. The hotter the CPU, the more you clip the CPU ratio. OCTVB is based on the by core usage Turbo Ratio configuration. For each number of active cores, you can define two temperature points, each with a unique number of “down-bins’. A down-bin is essentially the number of ratios you want to drop.
Note that on Alder Lake and Raptor Lake, OCTVB is only available for the P-cores and not for the E-cores.
The OCTVB function configures the ratio offsets on a by core usage basis. However, as we know from the Rocket Lake launch article, OCTVB also supports Per Core Ratio offsets. So, in theory, you can set a specific temperature-based down-bin for each P-core. The way it negotiates which ratio offset to apply in a given situation is to pick whichever is worse: the ratio offset as determined by the by core usage or the per core ratio limit offset. This feature is not exposed to the user in most BIOSes.
Overclocking Thermal Velocity Boost Configuration (Raptor Lake)
Let’s take this configuration of this OC Strategy as an example:
When 1 P-core is active, the base ratio is 61X, so the frequency is 6.1 GHz. However, when the temperature is 80 degrees Celsius, the ratio is clipped by 1X. That means the maximum ratio is now 60X.
When all 8 P-cores are active, the base ratio is 59X, so the frequency is 5.9 GHz. However, when the temperature is 70 degrees Celsius, the ratio is clipped by 2X. That means the maximum ratio is now 57X. When the temperature hits 90 degrees Celsius, the ratio is clipped once more by 1X. So, the resulting maximum ratio is now 56X.
Overclocking Thermal Velocity Boost Configuration (Rocket Lake)
You can use either XTU or, on motherboards that support it, configure Thermal Velocity Boost from the BIOS. The easiest way to understand the Thermal Velocity Boost configuration is by going from top ratio to bottom ratio.
The first column lists the count of active cores, going from 1 active core to 8 active cores with the 11900K.
The second column describes the maximum possible ratio for a particular count of active cores. So, in this example, the maximum ratio for 1 core active is 56 and the maximum ratio for 8 cores active is 53. Since we keep a fixed base clock frequency of 100 MHz, this results in respectively 5.6 GHz and 5.3 GHz.
The third column describes the first temperature offset point. When the CPU exceeds this temperature, it will decrease the ratio of the CPU. In my example, when 4 cores are active, and the CPU temperature exceeds 64 degrees then the CPU will decrease the ratio. Similarly, when the temperature exceeds 52 degrees and 8 cores are active, the CPU will also decrease the frequency.
The fourth column describes the ratio offset for the temperature configured in the third column. So, when the CPU temperature exceeds 64 degrees and 4 cores are active, the ratio will decrease by 1. 54 minus 1 equal 53. So, the CPU will run the 4 cores at 5.3 GHz.
The fifth column is an additional temperature offset point. The function is the same as the first temperature offset. While on Comet Lake the ratio offset for temperature B was fixed to 1, on Rocket Lake it is also configurable.
So, in this case, when 2 cores are active the frequency will be 5.6 GHz. However, if the CPU temperature exceeds 20 degrees, then the frequency will be 5.5 GHz. And if the temperature exceeds 45 degrees, the frequency will be 5.5 GHz.
Testing an OCTVB Configuration
Testing an OCTVB configuration is notoriously tricky because you can’t simply stress-test as you’d typically do. So, most of OCTVB validation is just running your benchmark test suite to see if there are any instabilities. Still, there is one technique we can use to get a rough idea of how many extra bins we can get with lower temperatures. That’s by relying on the Thermal Velocity Boost Voltage Optimizations.
I show an example in SkatterBencher #49.
When the voltage optimizations are enabled, we can use HWiNFO to track the CPU VID request as the CPU is heats up. The data collected shows an apparent increase in minimum, maximum, and average VID at a given temperature. The difference is about 50mV for 60 degrees Celsius.
When running a regression, the voltage decreases at about 1 mV per degree Celsius. Now we can combine this with the information from the CPU V/F curve where find an average of 29 mV step for each ratio increase between 54X and 60X.
So, we have an increase of 29 mV per CPU ratio and a decrease of 1 mV per degree Celsius. Thus, we can derive that at a given voltage, we can increase the ratio for every 29 degrees Celsius reduction in temperature.
Of course, this is a rough estimate, and nothing beats real-world testing. But hopefully, it can give you some idea of how to approach or get started with OCTVB tuning.
Intel OverClocking Thermal Velocity Boost in SkatterBencher Guides
We use Intel OverClocking Thermal Velocity Boost in the following SkatterBencher guides:
- SkatterBencher #53: Intel Core i9-13900KS Overclocked to 6300MHz (link)
- Let’s talk 6.7 GHz Core i9-13900KS Raptor Lake (link)
- SkatterBencher #52: Intel Core i9-13900K P-core Overclocked to 6500MHz (link)
- SkatterBencher #51: Intel Core i5-13600K Overclocked to 6200MHz (link)
- SkatterBencher #49: Intel Core i9-13900K Overclocked to 6100MHz (link)
- SkatterBencher #25: Intel Core i9-11900K Cryo Overclocked to 5600 MHz (link)
- SkatterBencher #19: Intel Core i9-10900K Overclocked to 6000 MHz (link)