kworker eating up cpu time when doing dd on 3.2.0 kernels

[Christian Brandes]

Hi Andy,

thanks for your first try to explain.

But on 3.0.0-13-generic my "dd" command makes about 75 MByte/s all the time.
On 3.2.0-10-generic it is 98 MByte/s until the cache is filled up and kworker captures my CPU. Then it continues at about 5MByte/s.

It is definitely not just that the load has moved. It is actually multiples higer.

Could you just try to reproduce that on a precise system?

Thanks!

Best regards
Christian

--- original mail: ---

> 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.

>>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.