I looks like the scheduler does not update internal timing information correctly.

I use the kernel from AM35x-OMAP35x-PSP-SDK-03.00.00.03 with the am3517_evm_defconfig. One example is the cyclictest from http://www.kernel.org/pub/linux/kernel/people/tglx/rt-tests/ (works without any RT patch). The CPU usage is always 0% and /usr/bin/time returns zero for system time even with extremely small intervals. When I run two applications, one that mostly runs in user space (e.g. summing up millions of ints) and one that mostly runs in kernel space (e.g. cyclictest). The one that runs in user space gets measurably slower if I start both programs at the same time, therefore I'm sure that the kernel space program wastes CPU cycles.