The instup.exe isn’t just the installation of the program function, it also handles the virus definition updates, shortly after you boot your system there will be a check for updates. Now depending on what other programs you have allowed to start on boot or they have set themselves to boot can mean there is rather a lot going on.

What is your operating system ?
What is your CPU and how much RAM do you have installed ?

I don’t know how the avast 9.0 auto updates work in comparison to avast 8 or earlier, but there used to be a resource limitation (I think 30%) so that it didn’t bog down the system. I would have though that wise limitation would/should have continued, but I don’t know if it did and I believe some Operating Systems didn’t support this resource limitation.

If the Repair suggested doesn’t work there are other things that can be considered, pruning those applications allowed to run on boot to essential and system only and possible delay the avast auto update check.