LP:470590 - Multiple fsync()s when sync_binlog=N (>0)

Depending on the setup and the choice of speed vs integrity in case of a server crash, configs need sync_binlog=1.
This slows down the server, but actually unnecessarily so. The setting apparently causes separate fsync() calls in various places in the code (binlog, relay log/index, possibly the master.info file), and that's ridiculous.

Can someone (Monty?) please fix this, and make the logic such that we get only a single fsync() per commit?
If this is a logistical problem given the XtraDB/InnoDB plugin, I can cope with one extra fsync() in the main server code in addition to the one in InnoDB... that can be a good intermediate step and would already reduce the overhead and slow-down significantly.

Thanks!