Bug#620297: base: vmstat and /proc/loadavg disagree

[Jonathan Nieder <jrnieder@gmail.com>]

tags 620297 + upstream
quit

Aman Gupta wrote:

> Incorrect load average:
> 2.6.32-bpo.5-amd64
> 2.6.32.55
> 2.6.32.55-620297patch
> 2.6.32.55-620297patch (nohz=off)
>
> Correct load average:
> 2.6.32.55-620297patch (CONFIG_NO_HZ=n)
>
> Since CONFIG_NO_HZ=y is default on the debian kernels, the two
> upstream patches alone are not going to be enough to fix this issue.

Thanks, Aman.  So it looks like this will need more investigation.

I assume kernels from sid do not have the same bug, right?  If so,
here's a quick way to narrow the problem down, if you'd like.

 1. Try the upstream kernel that introduced the "Cure more NO_HZ load
    average woes" fix:

	cd linux
	git checkout v2.6.37-rc7~13^2~5
	make silentoldconfig; # reuse configuration
	make deb-pkg; # optionally with -j8 or so
	dpkg -i ../<name of package>
	reboot

 2. Hopefully it does not reproduce the problem.  So try its parent:

	cd linux
	git checkout HEAD^
	make silentoldconfig; # reuse configuration
	make -j8 deb-pkg
	dpkg -i ../<name of package>
	reboot

    Hopefully it reproduces the problem.

If so, another test to try:

	cd linux
	git checkout v2.6.35-rc1~521^2~16
	git cherry-pick -x -s v2.6.37-rc7~13^2~5
	make silentoldconfig
	make -j8 deb-pkg
	dpkg -i ../<name of package>
	reboot

If that also works fine, the problem was introduced in backporting the
fix from 2.6.35 to 2.6.32.y --- either it has a missing prerequisite,
or there might be some small textual error.