armel/versatile: unknown HZ value 94

Does getconf CLK_TCK also report 94?

There is a relevant debian bug for this; http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=460331 which at least explains why this is reported as invalid.

A common way to compute this is to sleep 1 second and count the difference in timer interrupt events. procps similarly uses /proc/stat to get timer jiffy events, and /proc/uptime to get total system uptime. Roughly, by dividing jiffy events by uptime gives procps the tics per second value it uses, rather than any kernel HZ value actually set. In any case, however it is being derived, any HZ value between 66-94 ticks/second is currently considered invalid in procps, and any value between 95-105 is silently adjusted to 100. This 94 report could be some result of clock skewing under QEMU. The 2.6.30 arm kernel I use on qemu/versatile reports 100.

Decided to patch procps for a relaxed tick range.

note that the same occurs on imx51

There are reports of this happening native on i386 hw also. I extended the valid range from 95-105 to 90-105. This is not a great solution, because this really indicates the methodology presently used in procps is not sufficiently reliable, but it should be okay for those having this problem right now.

Looking at the Debian bug, two cleaner fixes seem to be proposed at the end of the bug trail. Let's try to use these instead of extending the HZ matching range.

This is a patch, for Karmic procps 3.2.8-1ubuntu1, that fixes the issue the way suggested at the end of the debian bug list, by assuring the linux version detection actually occurs before init_libproc, hence removing the hack calculation for modern kernels with elf notes. Originally, both init_Linux_version() and init_libproc() were attribute constructor functions, and hence depended on elf loader side effects as to whether the linux version code would happen to be called first. This patch resolves that issue, and I have verified the elf note method returns correctly, and with the 100hz tick value, for ARM kernels. One will also have to use update-initramfs to update the boot ramdisk image with the correct copy of procps binaries.

This bug was fixed in the package procps - 1:3.2.8-1ubuntu2

---------------
procps (1:3.2.8-1ubuntu2) karmic; urgency=low

  * New patch 60_linux_version_init, fixes linux version detection. This
    relied on a side-effect of the elf loader and previously hoped that
    constructors would be called in a certain order. That behavior was
    undefined and hence unreliable. For newer kernels, an elf note is now
    checked to extract HZ tick count. (LP: #364656).

 -- David Sugar <email address hidden> Thu, 06 Aug 2009 10:02:54 +0000