S7 - software redundancy


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I'm developing a program for two SOFTWARE REDUNDANT S7-315-2DP that are serving the same I/Os, which means they both will have atypical software.

I have some PID functions, so I have to use OB35.
The code I wrote is for PID loops and for some digital sequences. I did that before but not for redundant CPUs, and I used to put all PID functions in OB35 and all the other functions and function blocks in OB1. In software redundancy, FB101 must be invoked before and after the duplicated code (in my case PID & sequence).

The question is, is it right to leave OB1 empty and put all the code in OB35? If yes, how can I determine the OB35 cyclic interval??
Why not use OB35 for the loops that require a cyclic interrupt, and use OB1 for the loops and controls that can use a 'normal' PLC scan?

The code that I've written and maintained only used the cyclic OBs for the PID control functions.The rest of the code executes from OB1

I normally do what you do, but I don't know how it will work in redundancy. I mean if I have code in OB1 and code in OB35, where should I put FB101???
FB101 should be called in just one single block OB1 or OB35.