# kernel 2.6.25: successive slowdown w/ randomization [solved]

## mv

I observed a very strange problem on my x86 laptop which does not appear on the desktop although I use practically the same kernel configuration on both systems

(with hardened-sources-2.6.25, but I do not expect that "hardened" is the point here):

After some minutes of file-intensive working (e.g. an emerge world and emerging of a few small binary packages or a revdep-rebuild is enough) the system successively becomes dramatically slower, up to unusability: Even a simple shell loop (without any i/o) takes 10-50 times longer than usual.

There is no apparent reason: There is still the expected (sufficient) amount of free memory, and programs like htop show that e.g. the shell loop consumes most of the CPU power. The phenomenon only vanishes after a fresh boot.

The problem does not occur when I disable heap randomization (echo 0 >/proc/sys-kernel/randomiz_va_space; of course, I had an unset COMPAT_BRK .config option,

i.e. the content of this file is 2 by default). Since file access seems to play some role, I should mention that I use reiserfs.

Since I have a workaround and not much time, I am currently not too highly motivated to do further testing. Anyway, I would like to know if somebody else has the same problem or an immediate idea what might be wrong. Is perhaps heap randomization known to be buggy in 2.6.25?Last edited by mv on Tue Jul 01, 2008 10:49 pm; edited 1 time in total

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## TheAl

Many users reports slowdown with group cpu schudle. Try to change it to disable / enabled (one or both) :

```
CONFIG_CGROUPS is not set

CONFIG_GROUP_SCHED=y
```

Look at this thread :

https://forums.gentoo.org/viewtopic-p-5137295.html

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## mv

 *TheAl wrote:*   

> Many users reports slowdown with group cpu schudle. Try to change it to disable / enabled (one or both) :
> 
> ```
> CONFIG_CGROUPS is not set
> 
> ...

 

Thanks, I will give it a try if I find time to recompile. However, from the postings, it seems to be a different problem:

Once the slowdown "happened", it occurs even for even shell loops without any I/O and without any other processes running.

swap is not involved at all and I observe no disk access; there are also no processes waiting for I/O. It just appears that the processor has decreased its speed.

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## toralf

I'm pretty sure that CONFIG_FAIR_GROUP_SCHED is not what a user wants to set at a desktop system.

This option is rather designed to use at a server.

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## mv

Since now hardened-sources-2.6.25-r1 came out, I recompiled the kernel (now without CONFIG_CGROUPS and CONFIG_GROUP_SCHED) and after 10 minutes of testing the problem did not re-appear yet.

However, there were several bugfixes in this new kernel release anyway (both in the "hardened" part as well as in the vanilla part), so there are also quite some chances that one of those fixed it (I will not recompile the kernel with the previous settings just to try).

I will mark the topic as solved.

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