`getblock` is slow on verbosity, it's happened because `LOCK(cs_main)` applied for whole function including JSON generation
https://github.com/bitcoin/bitcoin/blob/ef70f9b52b851c7997a9f1a0834714e3eebc1fd8/src/rpc/blockchain.cpp#L810

I added few lines which print spent time:
```cpp
    LOCK(cs_main);
    auto t1 = std::chrono::high_resolution_clock::now();
...
    auto t2 = std::chrono::high_resolution_clock::now();
    auto ret = blockToJSON(block, pblockindex, verbosity >= 2);
    auto t3 = std::chrono::high_resolution_clock::now();
    std::cout << "blockToJSON " << pblockindex->nHeight << ": " << std::chrono::duration_cast<std::chrono::microseconds>(t2 - t1).count() << " " << std::chrono::duration_cast<std::chrono::microseconds>(t3 - t1).count() << std::endl;
    return ret;
```

and numbers looks like:
```
blockToJSON 570019: 14727 201870
blockToJSON 570022: 16049 225224
blockToJSON 570021: 33776 217398
blockToJSON 570020: 21754 191669
blockToJSON 570023: 30949 236941
blockToJSON 570025: 23346 223673
blockToJSON 570024: 18732 203002
blockToJSON 570026: 17467 216213
blockToJSON 570027: 16658 217395
blockToJSON 570028: 19015 219183
```

i.e. everything before JSON generation takes 15-30ms, while JSON takes minimum 190ms and lock `cs_main` for all this time. As result it's possible extract only ~5 blocks per second.

Looking on the code I think it's possible copy data from `CBlockIndex` to extra structure, so in this case `cs_main` can be unlocked right after `GetBlockChecked`.
https://github.com/bitcoin/bitcoin/blob/ef70f9b52b851c7997a9f1a0834714e3eebc1fd8/src/rpc/blockchain.cpp#L828
As result `getblock` in verbosity mode should be much faster (in case if `-rpcthreads` will be adjusted too).

Does this make sense?
}
        int64_t weight = 0;
        if (do_calculate_weight) {
            weight = GetTransactionWeight(*tx);
            total_weight += weight;
        }
        if (do_calculate_sw && tx->HasWitness()) {
            ++swtxs;
            swtotal_size += tx_size;
            swtotal_weight += weight;
        }
        if (loop_inputs) {
            CAmount tx_total_in = 0;
            for (const CTxIn& in : tx->vin) {
                CTransactionRef tx_in;
                uint256 hashBlock;
                if (!GetTransaction(in.prevout.hash, tx_in, Params().GetConsensus(), hashBlock)) {
                    throw JSONRPCError(RPC_INTERNAL_ERROR, std::string("Unexpected internal error (tx index seems corrupt)"));
                }
                CTxOut prevoutput = tx_in->vout[in.prevout.n];
                tx_total_in += prevoutput.nValue;
                utxo_size_inc -= GetSerializeSize(prevoutput, PROTOCOL_VERSION) + PER_UTXO_OVERHEAD;
            }
            CAmount txfee = tx_total_in - tx_total_out;
            assert(MoneyRange(txfee));
            if (do_medianfee) {
                fee_array.push_back(txfee);
            }
            maxfee = std::max(maxfee, txfee);
            minfee = std::min(minfee, txfee);