Calculating weight for CPU intensive hooks

Question

This wouldn't be a problem if the CPU-intensive code would be placed inside an extrinsic since we could benchmark it and get the accurate weight for the code.

But the problem is that we cannot benchmark a hook inside a pallet(e.g. We cannot benchmark the on_initialize hook AFAIU).

If the code inside the hook is intensive because of reads/writes from the runtime we can use the T::DbWeight::get().reads_writes(reads, writes) function which calculates the weight it takes for the specified number of reads&writes.

But what can I do if the code is actually CPU-heavy?

Answer 1

There is nothing stopping you from benchmarking the on_initialize hook.
The manual Read/Write stuff is just an approximation, so benchmarking it is better,
Since its a Hook and not a Call, you need to use the syntax for arbitrary code execution:

on_initialize {
    // Setup code
}: {
    Pallet::<T>::on_initialize(worst_block_number);
}

You can see this being done in the Lottery pallet. The generated weight functions are then used here.