Description of problem: Timer expires in a different rate depending on CONFIG_HZ. Version-Release number of selected component (if applicable): RHEL 5.3 XEN How reproducible: Below Steps to Reproduce: 1. Build two different kernels, one with 100HZ and the other is 1000HZ. 2. Install it to guest kernel on XEN. 3. Run a simple test program using nanosleep. Actual results: The kernel built with 1000 HZ wakes up faster than the kernel built with 100HZ. Expected results: Regardless HZ config, it should expires at the same rate. Additional info: Thisis RHEL kernel-xen does not set XEN periodic timer which is 100HZ by default. When kernel is configured other than 100HZ, then kernel initialization code should set periodic_period by using VCPUOP_set_periodic_timer op.
This is expected due to the way the timer infrastructure works in the RHEL 5 kernel. The non-xen kernel should show the same behaviour. Current upstream and Fedora use a tickless kernel, which will behave like you expect things to work. Backporting those changes would be way too invasive and risky for a RHEL 5 update.