Q: A process running in a session is consuming 100% of available CPU. I have Fair sharing of CPU Citrix policy enabled. I had expected that Fair sharing of CPU works in a manner where a CPU resource is divided equally with the amount of session. Why is that not happening?

A: This is a common misconception. A process running in user session could still consume up to 100% of CPU even when Fair sharing of CPU between sessions policy is enabled.

Even when Fair sharing of CPU is enabled, a CPU-intensive user can still monopolize the CPU until other users need CPU.
​At that point, CPU Utilization Management feature withdraws either enough CPU from the CPU-intensive user to meet the needs of the others, or enough CPU from the CPU intensive user so that users have their CPU entitlement. 

However there are scenarios that above concept may not work with CPU Utilization Management, because CPU Utilization Management alters process base priorities to conform a user’s CPU consumption and has no control over the thread priorities.

This is by design.

Example scenarios:

• A thread priority boost occurs within a process. The operating system triggers this.
• A thread priority is altered by SetThreadPriority() Win32API. The program code defines this.

This exception scenarios can be tested and confirmed by using a CPUStress.exe tool from Sysinternals.



 

Citrix is not responsible for and does not endorse or accept any responsibility for the contents or your use of these third party Web sites. Citrix is providing these links to you only as a convenience, and the inclusion of any link does not imply endorsement by Citrix of the linked Web site. It is your responsibility to take precautions to ensure that whatever Web site you use is free of viruses or other harmful items.

Also a deep dive information about CPU scheduling is provided from MSFT in the foillowing URL links.

Scheduling Priorities
https://msdn.microsoft.com/ja-jp/library/windows/desktop/ms685100(v=vs.85).aspx