Le lundi 22 mars 2010 à 11:17 +0100, Kristian Evensen a écrit : > Hello, > > I am currently comparing different IP-tunneling protocols/implementations, > and have stumbled upon something I am not able to explain. Regardless of > which tunneling technology I use, the latency increases with a couple of 10s > of ms and I see a significant degradation of throughput (compared to when no > tunnels are used). The only exception is IP-in-IP, where I get similar > performance with and without tunnels, but it does unfortunately not work in > my scenario. > > First, I thought this was caused by the different tunneling software, but > after measuring the processing time of the applications (xl2tp and > pptp-client) and when the packets are seen by the different iptables chains > (using LOG), these delays seem to be acceptable. However, one delay sticks > out. After the packet has been decapsulated and fed to PPP, it takes a > "long" time before it is seen again. My question is, can PPP be the cause of > the higher latency and lower throughput? > > Similar observations are made at both ends of the tunnel. A soon as a round trip on a user process is requested to handle a packet, you can have delay because of scheduling constraints. You could try latencytop and check if something strange raises, 10 ms seems excessive. IP-TIP tunnels dont use a user space program, they are immune to scheduler latencies. -- To unsubscribe from this list: send the line "unsubscribe linux-ppp" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
