Bridge unavailable during differential consensus update
After updating Tor from 0.3.0.9 to 0.3.1.4 (on a Raspberry Pi running Raspbian), I observed that my bridge became unable to answer new connection requests for extended periods, from 10 to 20 minutes or more, while tor process uses all available cpu (more than 90% on average - with no corresponding traffic for clients) and files are updated in /var/lib/tor/diff-cache directory. (For example, if I launch a TorBrowser using this bridge during such an update, it remains blocked before opening the Welcome window, and the corresponding client tor process remains blocked after "Bootstrapped 90%: Establishing a Tor circuit", for 10 minutes or more). So I had to downgrade to 0.3.0.9, so that my bridge doesn't become unavailable for a total of several hours per day.
May I suggest that an option make it possible to choose between the new differential update mode and the traditional one? First, this would be necessary for some (like me) to keep following new Tor versions long term. And even on more powerful platforms, and even if a better handling of priorities could make it possible for main Tor thread to remain available on Pi, Tor relay operators might want to make different choices between minimizing bandwidth for consensus transfer or minimizing cpu usage, and hence power consumption. (Please think of the Planet globally, and not only of the network ;) )