Originally Posted by meynaf
Try measuring the difference with some benchmark, and see if it's worth.
Well, it is personal taste but I always find it worth to disable the OS when it comes to time critical code because the OS does so much stuff in the background that you do lose time for your own code which I do not like. But, as so often, this is a matter of taste.
As for the lockup, maybe it's interrupt related? Just a shot in the dark but worth to check.