How Intel’s Core i7 Turbo Boost SPECIFICALLY works

by ThinkPads on December 4, 2009

turbo_3

Back in October we briefly covered Intel’s new Core i7 Turbo Boost feature, which allows for each of the four cores to be independently throttled to higher speeds based on demand and thermal load.

A few of you had questions on how exactly this would work and we just had another reader step up with some details on how/when the cores are throttled. I’ve reposted his original comment below for your absorption. If anyone has any additional clarification, please feel free to share in the comments!

The Core i7-720QM can use a maximum multiplier of 13, 13, 18 and 21 when 4, 3, 2 and 1 core are active.
In all Core i7 CPUs, the multiplier is completely dynamic and can be constantly changing. It can transition between the above 4 values hundreds of times a second based on load and how many cores are in the active state.
If you are running a single threaded activity and only a single core is in the active state, the multiplier can go as high as 21. If any background activity kicks in and wakes up a second core, the maximum multiplier will instantly drop to 18. If a third or fourth core becomes active then the maximum multiplier drops down to 13. As soon as the background tasks are completed, cores can go back to sleep which allows the maximum multiplier to increase. This is happening constantly.
Software like CPU-Z that samples the multiplier once per second might not give you a clear idea of what the constantly changing multiplier is up to. Intel recommends using the high performance timers within the CPU to accurately calculate the average multiplier over each 1 second interval. This method is outlined in the November 2008 Intel Turbo White Paper and is the method that both RealTemp and i7 Turbo use which can be downloaded from here.
http://www.fileden.com/files/2008/3/3/1794507/RealTempBeta.zip
i7 Turbo will clearly show you what each thread of your Core i7 CPU is up to.

unclewebb says:

The Core i7-720QM can use a maximum multiplier of 13, 13, 18 and 21 when 4, 3, 2 and 1 core are active.

In all Core i7 CPUs, the multiplier is completely dynamic and can be constantly changing. It can transition between the above 4 values hundreds of times a second based on load and how many cores are in the active state.

If you are running a single threaded activity and only a single core is in the active state, the multiplier can go as high as 21. If any background activity kicks in and wakes up a second core, the maximum multiplier will instantly drop to 18. If a third or fourth core becomes active then the maximum multiplier drops down to 13. As soon as the background tasks are completed, cores can go back to sleep which allows the maximum multiplier to increase. This is happening constantly.

Software like CPU-Z that samples the multiplier once per second might not give you a clear idea of what the constantly changing multiplier is up to. Intel recommends using the high performance timers within the CPU to accurately calculate the average multiplier over each 1 second interval. This method is outlined in the November 2008 Intel Turbo White Paper and is the method that both RealTemp and i7 Turbo use which can be downloaded from here.

http://www.fileden.com/files/2008/3/3/1794507/RealTempBeta.zip

i7 Turbo will clearly show you what each thread of your Core i7 CPU is up to.

Tagged as: turbo boost

Previous post:

Next post: