Windows Defender was found to affect Intel CPU performance

Recently, Kevin Glynn, the developer of software such as ThrottleStop and RealTemp, discovered during the development of the software that Windows Defender on Microsoft Windows 11 & Windows 10 would significantly affect the performance of Intel CPUs. While security software is bound to have a slight performance impact during real-time protection, this time the impact is much larger.

As reported by TechPowerup, Kevin Glynn found that HWiNFO reported a lower frequency when the CPU was fully loaded. The bigger problem is that when Windows Defender is affected, there is a noticeable drop in performance, such as a Core i9-10850K running at 5GHz at full core frequency, which loses 6% of performance. It is understood that whether it is a desktop platform or a mobile platform, Intel’s 8th, 9th, 10th, and 11th generation Core will be the same in Windows 11 & Windows 10, but to different degrees, and AMD’s processors will not be affected.

The root cause of consuming so much performance is that Windows Defender randomly uses all 7 hardware performance counters provided by Intel CPUs, including 3 fixed function counters. Each counter can be programmed in one of four modes to configure the privilege level for which it counts, including Disabled, OS (ring-0), User (ring>0), and All-Ring. Since these counters share resources, multiple programs may wish to access these counters at the same time.

System applications like HWiNFO or ThrottleStop set these counters to “mode 3” or “All-Ring”. After the same mode is set, it is no problem for multiple programs to use the same counter, but Windows Defender is set to “mode 2”, which leads to constant contention between programs, and the counter control register will constantly change between 0x222 and 0x332.

The root of the problem was not Intel’s hardware, as after manually configuring the settings, performance returned to normal without affecting Windows Defender’s virus protection. The temporary method is to use the Reset Counters button in the Counter Control tool to reset the counters with one click, or use the ThrottleStop tool and select the “Windows Defender Boost” function in the “Options”.