This statistic stores the number of times DBWR (not LGWR) takes a batch of dirty buffers and writes them to disk.
But if log_file_sync is high , you have to tune log_buffer
SELECT SUM(DECODE(name,'summed dirty queue length',value)) /
SUM(DECODE(name,'write requests',value)) "Write Request Length"
FROM v$sysstat WHERE name IN ( 'summed dirty queue length','write requests')
AND value > 0;
If this value is larger than 1/4(db_block_buffers) increase db_file_simultaneous_writes.