The queue depth can be read from /sys/bus/scsi/devices/*/queue_depth,
so don't log it.  And the hint about speed improvements is misleading,
at least under current kernels.  If serialization is switched off, read
performance is typically increased by less than 10%.  (I did not test
write performance recently.)  On the other hand, serialize_io=0 is not
yet safe due to some implementation issues that are not trivial to fix.
Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>