How to find out "InnoDB Write buffer efficiency"?
Why do you need to know it?  There is no actionable information in the statistic.

Make innodb_buffer_pool_size about 70% of available RAM (assuming more than 4GB of RAM); that will be optimal.

Look for slow queries and improve them; that will cut back on performance problems.

Here are some things you can get from SHOW GLOBAL STATUS and SHOW VARIABLES:


Innodb_pages_written / Innodb_buffer_pool_write_requests -- Write requests that had to hit disk -- &lt;15% is 'good'
Innodb_buffer_pool_wait_free / Innodb_buffer_pool_write_requests -- Should not have to wait to get into the buffer pool. -- &lt;1% is 'good'
Innodb_buffer_pool_pages_flushed / Uptime -- Writes actually going to disk
Innodb_buffer_pool_pages_flushed / max(Questions, Queries) -- Buffer pool writes per query