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Date: Fri, 11 Apr 2014 04:44:42 +0200 From: Hannes Frederic Sowa <hannes@...essinduktion.org> To: Eric Dumazet <eric.dumazet@...il.com> 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, Apr 10, 2014 at 06:42:10PM -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. > > Tested: > > ifconfig lo mtu 70000 > netperf -H ::1 > > Before patch : > > -> Throughput : 0.05 Mbits > > After patch : > > -> Throughput : 36624.24 Mbits > > Reported-by: Francois WELLENREITER <f.wellenreiter@...il.com> > Signed-off-by: Eric Dumazet <edumazet@...gle.com> Acked-by: Hannes Frederic Sowa <hannes@...essinduktion.org> Sorry about my wrong statement earlier in this thread, you're right. Btw. this patch fixes a flaw in the UDP output path, too, where we didn't generate EMSGSIZE error correctly before in all cases. udp_sendmsg only checks for INT_MAX - sizeof(udphdr) and defers further checking to ip6_append_data which seems to be prepared for jumbograms. ;) Very cool catch with the possible ipv4 performance improvment, too. ;) Thanks, Hannes -- 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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