zbd: count sectors with data for write pointer zones

zbd: count sectors with data for write pointer zones

ZBD fio code tracks 'sectors with data' for two different purposes.
The first one is to process zone_reset_threshold. When the ratio of
sectors with data in zones with write pointer goes beyond the specified
number, zone reset is triggered. The second purpose is to control the
direction of the first I/O of random mixed read/write workloads. If all
write pointer zones in the I/O range are reset at the beginning of such
a workload, fio has no data to read and will immediately end the run of
the test section. To avoid this, fio checks 'sectors with data' and if
it is zero (i.e. it is the very first I/O), it modifies the direction
of that I/O from read to write.

Currently, when the workload range includes both conventional and
sequential zones, all sectors in conventional zones are counted as
'sectors with data' along with sectors in sequential zones.
This leads to incorrect handling  of 'zone_reset_threshold' option -
zone reset timing of sequential zones is affected by the amount of
data read from or written to conventional zones. To avoid this,
conventional zones should be excluded from 'sectors with data'
calculation.

On the other hand, if the sectors of conventional zones were excluded
from the sectors with data, it could result in the wrong initial I/O
direction for random workloads. When the zones in I/O region are all
conventional, 'sectors with data' would always be zero. Because of
this, read operations are always changed to writes and reads are never
performed.

To avoid this contradiction, introduce another counter,
'wp_sector_with_data'. It works similar to the existing
'sectors_with_data', but it counts data sectors only in write pointer
zones. Use this newly introduced count for zone_reset_threshold checks
and keep on using the original count for the initial random I/O
direction determination.

When counting sectors with data, lock only write pointer zones, no need
to lock conventional zones.

Signed-off-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>
Signed-off-by: Dmitry Fomichev <dmitry.fomichev@wdc.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>