latency

1 ns cpu register
10 ns L1, L2
100 ns L3, Mem
1 us syscall
10 us context switch
100 us process http request，1MB Mem，8K SSD
1 ms ssd write, 内网 round trip， redis get
10 ms hard disk seek
100 ms 1GB Mem
1 s bcrypt a passwd, TLS handshake, 1GB SSD
10 s 10GB network