From mboxrd@z Thu Jan 1 00:00:00 1970 From: Kristian Evensen Date: Thu, 14 Jan 2010 22:19:05 +0000 Subject: PPP and buffer sizes Message-Id: <4B4F9859.1050909@gmail.com> List-Id: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: linux-ppp@vger.kernel.org Hello, I am trying to debug a performance issue I am experiencing with L2TP-tunnels (created using xl2tpd). When I measure the UDP-performance of different desired throughputs using iperf together with the tunnel, I see that the throughput stabilizes at a certain speed while the packet loss increases. When I measure the performance using TCP together with the tunnel, I see a very high number of packet losses, forcing congestion control and resulting in a significantly lower throughput than without tunneling. I guess this is caused by buffers being filled up and packets are dropped, however, I have not been able to figure out which buffer or exactly why this happens. If I remove the tunnels and measure the performance, the maximum supported throughput by the network is reached, so both the UDP and TCP send and receive buffers are big enough. I have also measured the processing delay caused by the L2TP-software and that is at most 50 microseconds, which should not affect the results. L2TP passes packets to PPP after they have been decapsulated and, as far as I have understood, PPP + IP layer processing (which is on microsecond scale) is the last step before the packet is sent to the application layer. My question is therefore, is there anything in PPP that can explain what I am experiencing? Thanks in advance for any help, Kristian