kworkers for dm-crypt locked to CPU core 0?

[Christian Schmidt <schmidt@digadd.de>]

Hi everyone,

I am trying to troubleshoot some strange performance issues I am seeing
on a machine of mine. Said machine had 10 drives mapped via separate
dm-crypt instances. The aggregate (read) throughput seems to hover
around 120-130MB/s (looking at iostat -x -d) when running an instance of
dd if=/dev/dm-<instance> of=/dev/null bs=1m for each mapping. However
"top" shows that one core is loaded with 99% system tasks, and two to
three cores are spinning in iowait. All the kworkers get their share of
roughly 10% CPU.

"taskset" shows that all of the kworkers have an affinity mask of 1, so
they can run on core 0 only, and trying to change it results in an error
of "Invalid argument".

Is there a way I can make the scheduler put those on multiple cores?

Please cc: me since I am not subscribed.

Regards,
Christian