rdtsc accuracy across CPU cores

Question

I am sending network packets from one thread and receiving replies on a 2nd thread that runs on a different CPU core. My process measures the time between send & receiv

Answer 1

I recommend that you don't use rdtsc. Not only is it not portable, it's not reliable and generally won't work - on some systems the rdtsc does not update uniformly (like if you're using speedstep etc). If you want accurate timing information you should set the SO_TIMESTAMP option on the socket and use recvmsg() to get the message with a (microsecond resolution) timestamp.

Moreover, the timestamp you get with SO_TIMESTAMP actually IS the time the kernel got the packet, not when your task happened to notice.