Red Hat Bugzilla – Bug 496354
Timer expires in a different rate depending on CONFIG_HZ
Last modified: 2009-04-17 21:32:20 EDT
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
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.
The kernel built with 1000 HZ wakes up faster than the kernel built with 100HZ.
Regardless HZ config, it should expires at the same rate.
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.