high CPU DBW process

On a 19.16 database on Solaris Sparc64 we have the following:

One of the databases running on that machine, is taking huge amounts of CPU time.

The database is up for about 2 weeks, but the Database Writer proces ( ora_dbw0_$ORACLE_SID ) has taken more than 1000 minutes of CPU time (which is more than 16 hours).

The process itself (v$processes) cannot be linked to a session (v$session), because it's a special one.

But my question is now obviously: what is it doing ? How do I find why it is taking this amount of time ?

If you calculate, it is taking 71 minutes of CPU time per day.