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Date: Thu, 10 Apr 2014 20:14:50 -0700 From: Eric Dumazet <eric.dumazet@...il.com> To: Hannes Frederic Sowa <hannes@...essinduktion.org> Cc: YOSHIFUJI Hideaki <yoshfuji@...ux-ipv6.org>, 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 Fri, 2014-04-11 at 04:57 +0200, Hannes Frederic Sowa wrote: > On Fri, Apr 11, 2014 at 11:30:44AM +0900, YOSHIFUJI Hideaki wrote: > > Eric Dumazet wrote: > > > > > 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. > > > > It is a TCP issue. We should not limit the mtu to 65532+40. > > I am for 65535+40. Otherwise, other protocol such as UDP cannot > > use full mtu as before. > > I have not seen problems with max ipv6 mtu limit of 65535+40 and tcp. > > I agree this would be a better approach, and maybe & ~3 the mtu/mss > in tcp code? I assume people expect maximum udp packet sizes working > over loopback? Yes, recent Intel cpus have really fast mem copy, even with different alignments for source/dest. But old cpus or other arches might have an issue here. Apparently nobody really cares, so I wont argue and send a V2. -- 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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