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Date: Thu, 10 Apr 2014 18:58:45 -0700 From: Eric Dumazet <eric.dumazet@...il.com> To: Hannes Frederic Sowa <hannes@...essinduktion.org> Cc: David Miller <davem@...emloft.net>, Francois WELLENREITER <f.wellenreiter@...il.com>, netdev@...r.kernel.org Subject: Re: [PATCH] ipv6: Limit mtu to 65572 bytes On Thu, 2014-04-10 at 18:42 -0700, Eric Dumazet wrote: > From: Eric Dumazet <edumazet@...gle.com> > > Francois reported that setting big mtu on loopback device could prevent > tcp sessions making progress. > > We do not support (yet ?) IPv6 Jumbograms and cook corrupted packets. > > We must limit the IPv6 MTU to (65535 + 40) bytes in theory. > > In practice, its better to align to a multiple of 4 for optimal TCP > performance. Same story for IPv4 btw : current lo mtu=65536 is suboptimal lpq83:~# ifconfig lo mtu 65536 lpq83:~# ./netperf MIGRATED TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to localhost () port 0 AF_INET Recv Send Send Socket Socket Message Elapsed Size Size Size Time Throughput bytes bytes bytes secs. 10^6bits/sec 87380 16384 16384 10.00 33020.76 lpq83:~# ifconfig lo mtu 65533 lpq83:~# ./netperf MIGRATED TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to localhost () port 0 AF_INET Recv Send Send Socket Socket Message Elapsed Size Size Size Time Throughput bytes bytes bytes secs. 10^6bits/sec 87380 16384 16384 10.00 39010.09 -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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