- Jun 1, 2008
- 1,141 (0.33/day)
This tool is designed to test for Turbo throttling which can occur on some X58 motherboards when overclocking at high load levels as you approach the TDP limit of your CPU. Most motherboards allow you to turn off TDP based throttling in the bios but not all of them do and not all bios versions work correctly. If you are using the Turbo feature of a Core i7 processor, it's a good idea to make sure that your motherboard properly supports this feature.
The multiplier for a Core i7-920 is typically 20.0 and if Turbo mode is enabled, you get a +1.0 boost for a total of 21.0. With a 920, even if a bios lets you select a multiplier of 21.0 directly, internally it is still using the Turbo feature of your CPU. Turbo throttling can occur at high loads where the +1.0 Turbo boost will start to rapidly cycle on and off hundreds of times a second as you approach the TDP limit. When this first starts to happen, not all software is able to detect that your multiplier is intermittently dropping down to 20.0. Software that only samples your multiplier once per second might completely miss this problem.
There are two ways to read the current multiplier from a CPU. The typical way is to read a model specific register (MSR) within the CPU. This gives you a snapshot of what the multiplier is at that particular instant. If software only reads this value once per second then it can miss what's really going on.
The second way that Intel recommends is to compare two high performance internal timers within their CPU and then to use that information to calculate what the multiplier is.
The Intel Turbo White Paper outlines this method:
The advantage of the calculated multiplier is that during a one second sample period, it can be used to very accurately calculate the average multiplier during that interval. This method tends to be extremely precise when the CPU is fully loaded.
On a Core i7-920 at full load with the Turbo fully engaged, both the Calculated Multiplier and the MSR Multiplier should be firmly locked on 21.000. At full load, if either multiplier starts to drop, that is an excellent warning sign that Turbo throttling is starting to occur.
For the MSR based multi, I am sampling it once per thread per second to improve its accuracy. If you have hyper threading enabled and it samples 7 of your threads at a multiplier of 21.0 but the eighth thread has dropped down to 20.0 by the time it gets sampled, then it will display 20.875 showing that the Turbo was mostly enabled during that sample period. On Core i7, the multiplier is a whole number and at any instant in time it will be the same for each thread but with multiple samples during a one second interval, we should see better results from the MSR based multiplier.
For severe cases, both multipliers will drop down to 20.000 and clearly show Turbo throttling in progress. Other times, maybe the calculated multiplier will give you an earlier warning of this problem.
Both multipliers and the Average CPU Load can be logged for further analysis. The load of each thread is displayed in the GUI. While testing, you can easily add a note directly to your log file like, "Started Prime95" or "Started LinX." You can use either the Enter key or click on the Add Log Note button.
The EIST section reads this information directly from the CPU. If it disagrees with what you set in the bios then that's usually a sign that your bios is not turning off this feature.
The Load Filter option for the Calculated Multiplier lets you weed out any bad data from the Min and Max areas that can occur with this method when the CPU is lightly loaded. If you set it to 0% then all calculated multiplier data will show up in the Min/Max area. If you use 90% then data will only be added to the Min/Max area if the CPU load is 90% or greater. I added this option so if you're gaming, light load between rounds or when going back to the desktop won't interfere with your Min/Max results.
The Asus P6T Deluxe does not give users the option to disable TDP based Turbo throttling in the bios. Most boards have this option but it's always a good idea to check your board and bios settings to make sure this feature works.
Many thanks to rge at XtremeSystems for helping to thoroughly test this tool. His Gigabyte board used to have Turbo throttling issues too until the bios guys listened to the complaints and fixed the problem.