kworker eating up cpu time when doing dd on 3.2.0 kernels

[Andy Whitcroft]

On Fri, Jan 27, 2012 at 05:37:15PM +0100, Christian Brandes wrote:
> Hi all!
> 
> I found an issue with kworker on kernel versions: 3.2.0-10-generic, 3.2.0-8-generic and 3.2.0-2-generic.
> 
> When I do "dd if=/dev/zero of=/tmp/zero1.tmp bs=1024 count=13000000" kworker threads start eating up my CPU-time as described in: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/887793 posting 22 and 23.
> 
> Older kernel versions do not seam to be affected like 3.0.0-13-generic.
> 
> Can anyone help me?

I would expect to find that in older kernels other threads are taking on
the load.  Presumably they are flushing pages like mad to make space in
cache for your workload.  I guess I am asking, is the overall load
actually higher, or just moved.

-apw