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Date: Thu, 30 May 2019 16:56:15 -0700 From: Eric Dumazet <eric.dumazet@...il.com> To: Alexander Duyck <alexander.duyck@...il.com>, Stephen Hemminger <stephen@...workplumber.org> Cc: Eric Dumazet <edumazet@...gle.com>, Paul Menzel <pmenzel@...gen.mpg.de>, Jeff Kirsher <jeffrey.t.kirsher@...el.com>, intel-wired-lan <intel-wired-lan@...ts.osuosl.org>, netdev <netdev@...r.kernel.org>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org> Subject: Re: Driver has suspect GRO implementation, TCP performance may be compromised. On 5/30/19 3:52 PM, Alexander Duyck wrote: > Actually I think there are some parts that don't have any receive > limits that are supported by the e1000 part. What ends up happening is > that we only drop the packet if it spans more than one buffer if I > recall correctly, and buffer size is determined by MTU. > > I always thought MTU only applied to transmit since it is kind of in > the name. As a result I am pretty sure igb and ixgbe will be able to > trigger this warning under certain circumstances as well. Also what > about the case where someone sets the MTU to less than 1500? I think > most NICs probably don't update their limits in such a case and > wouldn't it also trigger a similar error? > Linux does not have a notion of MRU, mtu is used for both tx and rx. Most NIC drivers allocate skb of the maximal size (derived from netdev->mtu) and program the NIC to drop packets bigger than X bytes (X also derived from netdev->mtu) Another interesting point is that Paul host is receiving big packets, that means that one host in his local network is overriding the 1500 MTU :) Eventually we could add a netdev->mru and allow few drivers to set their maximal mru, if bigger than netdev->mtu. e1000e would probably set netdev->mru to 2048 - sizeof(ethernet headers), if the driver is operating at MTU = 1500
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