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Message-ID: <20100829095951.GA3153@del.dom.local> Date: Sun, 29 Aug 2010 11:59:51 +0200 From: Jarek Poplawski <jarkao2@...il.com> To: David Miller <davem@...emloft.net> Cc: shemminger@...tta.com, eric.dumazet@...il.com, herbert@...dor.apana.org.au, netdev@...r.kernel.org Subject: Re: [RFC] gro: Is it ok to share a single napi from several devs ? On Sat, Aug 28, 2010 at 02:41:30PM -0700, David Miller wrote: > From: Stephen Hemminger <shemminger@...tta.com> > Date: Sat, 28 Aug 2010 10:14:24 -0700 > > > The Marvell Yukon2 hardware supports two interfaces sharing a common interrupt. > > Therfore the sky2 driver has up to two net devices and a single NAPI per board. > > It is possible in a single invocation of the poll loop to process frames > > for both ports. GRO works by combining received packets from identical > > flows over one NAPI interval. It is possible on sky2 that one packet > > could be processed for the first port, and the next packet processed was for > > second port and the two packets were related so that GRO would combine them. > > The check for the same dev is required to prevent this. Yes it is an unlikely > > corner case, but the purpose of GRO is to do aggregation but preserve the > > flow characteristics of the incoming traffic. > > If that is true then GRO is going to refuse to merge every single > frame that arrives on the second port of a SKY2 device. :-) > > This is because for the two ports, you allocate and register one NAPI > instance which uses only the first port's netdev pointer. > > Therefore, when GRO compares napi->dev to skb->dev it will always not Actually, when GRO compares napi->dev to skb->dev? Jarek P. > match for packets coming from the second port since the netdev pointer > in skb->dev will be different. > > Since netpoll does similar things, this means both NAPI and netpoll > cannot function properly with SKY2's second port. It will only work > right on the first port. > > -- 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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