Greetings

I'm diagnosing why my application is slow and I found the problem by writing a simple TCP client/server, where each side sends/receives 64k at a time.

The bottleneck is on the receiving end, which uses has a Realtek 8139 100Mbit/s NIC and running Windows 7. I'm able to get 11.9 MiB/s as expected, but the CPU usage is very high - 80% on 0th CPU and ~20% on 1st CPU. Task manager shows conhost.exe taking 25% CPU and 10% for my program.

When I try the same receiving program on Debian, I can still get 11.9 MiB/s, but the CPU usage is now only 1% (user & system).

On the sending side, the CPU usage is practically 0% in both Windows 7 and Debian.

I tried changing the TCP receive/send buffer sizes and disabled internet connection sharing (does extra packet processing?) on the receiving end, but it doesn't help.

Any ideas?

I've seen this with video cards. Something looks like it's being simulated in software, or done very inefficiently.

OK, solved. The high CPU was due to doing 150 printf() /second. This was suggested by the large CPU usage by conhost.exe (handles console applications?)