Sandy Bridge Turbo Boost - how long can it be active?

[Fjodor2001]

Hi,

I just wonder how long the Turbo Boost in the Sandy Bridge CPUs can be active? Can the CPU stay in Turbo Boost mode as long as there is sufficient cooling and the CPU temperature does not rise above a certain threshold? Or what triggers the CPU to exit Turbo Boost mode (when the CPU is still under full load)?

Also, how does the CPU determine if the Turbo Boost shall be enabled for 1, 2 or 4 cores and/or the IGP?

Thanks!

 

[Zap]

Can the CPU stay in Turbo Boost mode as long as there is sufficient cooling and the CPU temperature does not rise above a certain threshold?
...
Also, how does the CPU determine if the Turbo Boost shall be enabled for 1, 2 or 4 cores and/or the IGP?

AFAIK as long as temperatures and power load (which can be adjusted in BIOS/UEFI) stay within thresholds, it can turbo forever. It turbos only the cores that have a load.

 

[IntelUser2000]

Sandy Bridge has two type of Turbo speeds:

-Infinitely sustainable
-Time, thermal, and power limited

For the 2600K it works like this:

3.5GHz(4 core, speeds are greater for less cores active) for indefinite periods of time. 3.8GHz for brief periods, I don't know the exact time, but its pretty short, Anandtech's 25 second mention is probably right. For low power SKUs or mobile ones the temporary boost is higher. Mobile ones can sustain it for maximum of 30-60 seconds depending on the SKU.

Steps into Turbo:
1. Sustained Turbo plus....
2. The temporary Turbo...
3. Duration determined by...
4. Temperature/Cooling

Steps out of Turbo:
1. Is the cooling solution better/worse than what the CPU can dissipate at maximum Turbo?
2. If its better, it'll stay at the enhanced Turbo speeds until the fixed timer ends
3. If its worse, the CPU will calculate how long it can stay before it heats up too much.

The gains for CPU Turbo Mode on regular voltage SKUs are in reality not much better than the one in Bloomfield.

 

[Mark R]

Also, how does the CPU determine if the Turbo Boost shall be enabled for 1, 2 or 4 cores and/or the IGP?

Just to add to what has been said. The infinitely sustainable turbo, like the standard Core i7 series, is active when the CPU is partially idling.

So, if only a single core is being used on a quad core, that core can receive a good turbo boost. If 2 or 3 cores are being used, then those cores can receive a smaller turbo boost. If all 4 cores are being used, then usually no turbo will be used - but if the core isn't working to its full capacity (e.g. the program is not using the FPU) then a small turbo boost may be available.

The amount of turbo available is determined by the a special turbo management processor built into the CPU. This measures voltages, currents, temperatures, rate of temperature rise, etc. and determines how much boost is safe to give (up to a certain maximum limit).

On a 95W CPU, the turbo management processor won't allow the total power consumption of the chip to go above 95W (to ensure that a heatsink designed for 95W won't overheat). If the turbo managment unit determines that the CPU is too hot (because the heatsink is inadequate), then it will reduce the boost.

The new feature on Sandy bridge is a 'temporary' turbo boost. This takes advantage of the fact that if the heatsink is cold (because the CPU has been idle) then it will take 15-25 seconds to warm up.

Sandy bridge turbo takes advantage of this to 'over boost' the CPU temporarily, if the CPU core temperature is lower than normal operating temperature. So, if you have a 95 W sandy bridge CPU, and it is cold, then the turbo unit can give an extra boost, ignoring the power limit - e.g. allowing the chip to use 110 W for a short period. While the heatsink may not be able to cope with this heat load indefinitely - you can get away with it for 15-25 seconds until the CPU cores reach normal operating temperature. Once normal operating temperature is reached (or after a time limit built into the CPU, or if the turbo management unit detects core temperatures rising too fast) the extra boost will be switched off, and the normal turbo mode restored.

If there is imbalance between GPU load and CPU core load, then the turbo managment unit will boost the component that has the highest load. So, if the CPU cores are maxed, but the GPU idle, the boost (if available) will go to the CPU cores. If the CPU cores are partially idle, but the GPU is maxed, the boost will go to the GPU.

 

[jimhsu]

During (BIOS controlled Turbo) overclocking, the turbo frequency stays at the same (e.g. 45x) as long as the chip is within thermal constraints. I think the scaling only occurs with the poorly-named "OS controlled Turbo" feature - aka controlling the maximum turbo frequency as a function of the number of cores.

With a decent heat sink, the CPU will probably never reach a temperature that requires it to throttle down due to exceeding TDP. I have a scientific app running here for 24+ hours using all 4 cores with a chip clocked to 45x, and temperatures have been below 50C. Didn't see any throttling.

 

[aigomorla]

theres a time limit on turbo?

WTF?

Is there an internal cycle counter which counts all the cycles its at turbo?

The only limitations on turbo i can think of is heat.
It will hit turbo as much as needed until you reach a temp threshold known as throttling.
Then you'll downclock.

But to my understanding there is no time limit to turbo.
If there was, we would only have 30 min overclocks.

 

[Fjodor2001]

During (BIOS controlled Turbo) overclocking, the turbo frequency stays at the same (e.g. 45x) as long as the chip is within thermal constraints. I think the scaling only occurs with the poorly-named "OS controlled Turbo" feature - aka controlling the maximum turbo frequency as a function of the number of cores.

With a decent heat sink, the CPU will probably never reach a temperature that requires it to throttle down due to exceeding TDP. I have a scientific app running here for 24+ hours using all 4 cores with a chip clocked to 45x, and temperatures have been below 50C. Didn't see any throttling.

I just wonder, does "BIOS controlled Turbo overclocking" mean that the CPU will stay in Turbo Mode as long as the CPU is within the thermal constraints (and there is CPU load that benefits from Turbo Mode)? I.e. there is no fixed max time that the CPU may stay in Turbo Mode? To me that sounds ideal. Why didn't Intel design it that way? Is there any drawback to such a solution?

Also, when people overclock their Sandy Bridge CPU using normal overclocking (i.e. not "BIOS controlled Turbo overclocking") to e.g. 4.5 GHz, is the Turbo Mode turned off then? Or will the CPU run at frequencies above the base frequency (e.g. 4.5 GHz) if overclocked and it enters Turbo Mode?

 

[jimhsu]

I just wonder, does "BIOS controlled Turbo overclocking" mean that the CPU will stay in Turbo Mode as long as the CPU is within the thermal constraints (and there is CPU load that benefits from Turbo Mode)? I.e. there is no fixed max time that the CPU may stay in Turbo Mode? To me that sounds ideal. Why didn't Intel design it that way? Is there any drawback to such a solution?

Also, when people overclock their Sandy Bridge CPU using normal overclocking (i.e. not "BIOS controlled Turbo overclocking") to e.g. 4.5 GHz, is the Turbo Mode turned off then? Or will the CPU run at frequencies above the base frequency (e.g. 4.5 GHz) if overclocked and it enters Turbo Mode?

This is the screen I'm talking about:

Unfortunately the crappy manual is not much help here. Seriously, most of the BIOS explanations in the manual look like this:

[Enable Turbo Mode]: Enables the Turbo Mode Feature.
[Load Line Calibration]: Sets Load Line Calibration for the processor.

And it might just be me, but I think it's really stupid to put the only important overclocking feature (Turbo) not in AI Tweaker, or CPU configuration, but CPU Power management?! User design fail.

 

[IntelUser2000]

theres a time limit on turbo?

WTF?

Is there an internal cycle counter which counts all the cycles its at turbo?

The only limitations on turbo i can think of is heat.
It will hit turbo as much as needed until you reach a temp threshold known as throttling.
Then you'll downclock.

But to my understanding there is no time limit to turbo.
If there was, we would only have 30 min overclocks.

Well, for overclockers like you, they'll set the TDP settings so it won't reach that and can sustain it forever. And that screenshot is also showing time parameters. "Short" equals temporary boost, and "Long" equals permanent boost.

 

[SlitheryDee]

I haven't messed with any of the Turbo mode parameters in the bios. During stress testing I haven't observed any drop off from the overclock that I set even though the temps did get uncomfortably high at times. If turbo mode is at least partially governed by TDP; at what point would I see throttling? Max temps I saw were in the mid-70s BTW.

 

[Arkainium]

This is the screen I'm talking about:

Unfortunately the crappy manual is not much help here. Seriously, most of the BIOS explanations in the manual look like this:

[Enable Turbo Mode]: Enables the Turbo Mode Feature.
[Load Line Calibration]: Sets Load Line Calibration for the processor.

And it might just be me, but I think it's really stupid to put the only important overclocking feature (Turbo) not in AI Tweaker, or CPU configuration, but CPU Power management?! User design fail.

If Long Duration Power Limit is left on auto does that mean that the board will restrict the CPU TDP to 95 watts? I have mine set to auto, and it never seems to go above 95 W in CPUID Hardware Monitor (not sure how accurate this is) despite being overclocked to 4.4 GHz. Should I increase it?

 

[BababooeyHTJ]

I'm actually trying to get turbo boost set up right now. I came across this thread with a little googleing. I have the 1 and 2 core limit set to a higher multi than I have the 3 and 4 core limits set to and it doesn't appear to be kicking in. It looks like I need to adjust these power limits, I could be wrong. I haven't seen a good explanation of these power limit settings and quite frankly I'm not sure what I could be doing wrong.

 

[IntelEnthusiast]

Very good answers you guys for you can read more on the Turbo Boost Technology at http://www.intel.com/technology/turboboost/.

Christian Wood
Intel Enthusiast Team