I bought new Lenovo laptop a week ago. At first it works very well but then suddenly it started to work very slowly. After installing CPU-Z, I found that the CPU multiplier is set to 4 (from 28).
I cannot find any option to change back it to 28 even in the BIOS. I haven't done any heavy tasks such as gaming.
Your problem will be fixed by unchecking BD PROCHOT.
Source "BD PROCHOT is not the same as PROCHOT. If your CPU gets too hot ( PROCessor HOT ) your CPU will slow down to protect itself from damage whether BD PROCHOT is enabled or disabled." So it is safe to uncheck BD PROCHOT and leave it unchecked. The BD PROCHOT setting seems to be common in Skylake CPU's, which is what you happen to have.
The purpose of BD PROCHOT (bi-directional prochot) is to force your CPU to underclock in order to let the entire PC cool down. From what I have found on several forums, it seems the setting is triggered too easily, causing it to throttle down when it doesn't need to be. As well as not turning off once it is cooled down.
BD PROCHOT allows your motherboard to throttle the CPU, rather than leaving that decision up to the CPU itself. PROCHOT will kick in when your CPU reaches it's max TDP which is either 100C or 105C, depending on the CPU. It also sounds like not many motherboards have the BD PROCHOT setting, but for the ones that do, many people have also experienced their CPU getting stuck at something under 1 GHz, usually in the 400-800 MHz frequency range.
You can probably uninstall OBSIDIAN, if you want. It would be nice to experiment and see if the laptop continues to function properly without it. If you wish, you may also leave it installed and just make sure it does not start when Windows boots. Then you can refer to the program in the future if needed.
Thank you @DrZoo I have fixed problem by installing OBSIDIAN program (see attached screenshot) download by link techpowerup. I unchecked "BD PROCHOT" checkbox and it fix problem. After that I can see in cpu-z 28 multiplier.
About "BD PROCHOT" I found this link
BD PROCHOT stands for bi-directional prochot. PROCHOT stands for processor hot which is the signal that is activated within the CPU when it reaches approximately 100C to 105C depending on the model number. This signal is what initiates thermal throttling so the CPU can slow down and keep from over heating. Intel included a bi-directional feature so if something else like a GPU is running too hot, it would be able to send a PROCHOT signal directly to the CPU and force it to cool down so the entire laptop cools down. Very few laptops seem to use this type of throttling. This feature was added for the Asus G51. Disabling this will allow your CPU to continue to run at full speed. Disabling this will not prevent your CPU from thermal throttling at its normal Intel set thermal throttle temperature. By default this is locked and you will need to go into the Options window to unlock it so you can toggle it on and off.
Your processor is an i5-6200U, which is not overclockable. Recent Intel processors with the 'K' suffix like the Core i7-7700K are overclockable. Generally, laptops do not have overclockable processors. The 'U' suffix indicates that it's made for low power consumption. Intel source on naming conventions : https://www.intel.com/content/www/us/en/processors/processor-numbers.html
