In this case, a colleague of mine was complaining that her workstation was running very slow even tough the workstation was memory upgraded. Since the term "running slow" is very relative, I needed info about the hardware and OS. The operating system was Windows 8.1 Enterprise x64, and hardware was HP ProDesk 600 G1.
The reason for this "running slow" behavior was the CPU usage of system interrupts process. 20-30% of the CPU usage was dedicated to this process all the time. From my experience the reason for this kind of behavior is hardware or driver related. The OS was fully patched with latest updates. So, I've started updating the drivers and BIOS. After updating the drivers and BIOS to the latest HP official versions the behavior was still the same, system interrupts process was holding 20-30% of the CPU. There were no pending restarts. And, the CPU usage behavior was the same on every restart. This behavior of high CPU usage from System Interrupts process has stopped, when I have shut down and power on the workstation. It's very strange, but I have successfully succeeded to reproduce this behavior on this HP model PC. And, this is the scenario when this high CPU usage of system interrupts process will happen for this PC model:
Whenever there is memory size change, BIOS will "alert 164 memory size error " press F1 to continue, the OS will boot and system interrupts process will run high CPU usage. This behaviour will continue, even if the OS is restarted several times. But, if you shut down, and power on the workstation, the CPU usage will be back to normal !
I'll call this a bug, so in case you're doing memory upgrade on this PC model, do not forget to power off and power on the PC after successful memory upgrading.
The reason for this "running slow" behavior was the CPU usage of system interrupts process. 20-30% of the CPU usage was dedicated to this process all the time. From my experience the reason for this kind of behavior is hardware or driver related. The OS was fully patched with latest updates. So, I've started updating the drivers and BIOS. After updating the drivers and BIOS to the latest HP official versions the behavior was still the same, system interrupts process was holding 20-30% of the CPU. There were no pending restarts. And, the CPU usage behavior was the same on every restart. This behavior of high CPU usage from System Interrupts process has stopped, when I have shut down and power on the workstation. It's very strange, but I have successfully succeeded to reproduce this behavior on this HP model PC. And, this is the scenario when this high CPU usage of system interrupts process will happen for this PC model:
Whenever there is memory size change, BIOS will "alert 164 memory size error " press F1 to continue, the OS will boot and system interrupts process will run high CPU usage. This behaviour will continue, even if the OS is restarted several times. But, if you shut down, and power on the workstation, the CPU usage will be back to normal !
I'll call this a bug, so in case you're doing memory upgrade on this PC model, do not forget to power off and power on the PC after successful memory upgrading.
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