There are some potential feefilter cleanups mentioned and motivated in comment https://github.com/bitcoin/bitcoin/pull/21509#issuecomment-805808485 . If you address the locking one, please be careful and make sure that `round()` is only called under a lock. See https://github.com/bitcoin/bitcoin/pull/21509#issuecomment-807992199

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std::string sProblem;
        if (nAvail >= sizeof(nonce)) {
            vRecv >> nonce;
            
            if (peer->m_ping_nonce_sent != 0) {
                if (nonce == peer->m_ping_nonce_sent) {
                    
                    bPingFinished = true;
                    const auto ping_time = ping_end - peer->m_ping_start.load();
                    if (ping_time.count() >= 0) {
                        
                        pfrom.PongReceived(ping_time);
                    } else {
                        
                        sProblem = "Timing mishap";
                    }
                } else {
                    
                    sProblem = "Nonce mismatch";
                    if (nonce == 0) {
                        
                        bPingFinished = true;
                        sProblem = "Nonce zero";
                    }
                }
            } else {
                sProblem = "Unsolicited pong without ping";
            }
        } else {