Macro frame_benchmarking::add_benchmark

macro_rules! add_benchmark {
    ( $params:ident, $batches:ident, $name:literal, $( $location:tt )* ) => { ... };
}

This macro adds pallet benchmarks to a Vec<BenchmarkBatch> object.

First create an object that holds in the input parameters for the benchmark:

let params = (&pallet, &benchmark, &lowest_range_values, &highest_range_values, &steps, repeat);

Then define a mutable local variable to hold your BenchmarkBatch object:

let mut batches = Vec::<BenchmarkBatch>::new();

Then add the pallets you want to benchmark to this object, including the string you want to use target a particular pallet:

add_benchmark!(params, batches, b"balances", Balances);
add_benchmark!(params, batches, b"identity", Identity);
add_benchmark!(params, batches, b"session", SessionBench::<Runtime>);
...

At the end of dispatch_benchmark, you should return this batches object.