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Date: Tue, 05 Jan 2010 17:33:38 -0800 From: Rick Jones <rick.jones2@...com> To: David Miller <davem@...emloft.net> CC: dhananjay.phadke@...gic.com, shemminger@...tta.com, amit.salecha@...gic.com, netdev@...r.kernel.org Subject: Re: [PATCH NEXT 0/2] qlcnic: Add Qlogic 1/10Gb Ethernet driver for CNA devices David Miller wrote: > From: Dhananjay Phadke <dhananjay.phadke@...gic.com> > Date: Tue, 5 Jan 2010 15:55:10 -0800 > > >>The LRO you are talking about was still kernel based >>LRO. Even GRO doesn't save PCIe transactions as much >>HW LRO does. That is the key. The difference between >>HW LRO and GRO is significant to keep former alive >>for a while. Is it really the PCIe transactions (*)? ISTR that HW LRO also tended to significantly cut-down on the ACK rate, rather like the oft-derided ACK avoidance heuristics in Solaris, HP-UX and various MacOSX revs. rick jones * OK, I am recalling that long ago and far away, the Alteon AceNIC (PCI) had very high DMA setup times - so long that if an outbound (in this case) packet was more than 1.something buffers the card was unable to acheive link-rate with a 1500 byte MTU. It meant that for straight copy outbound was fine, but for copy avoided (eg sendfile() - this was HP-UX 11) one was sub-par because it was at least two buffers per packet - aka two DMA setups - and sometimes three. One workaround was to use JumboFrames - the larger MTU helped. > > > But HW LRO is not bridge/forwarding/etc. agnostic because it loses > information. > > As soon as I turn on forwarding to make a NAT box or whatever, all of > the hw LRO gets turned off and we're back to square one for local > connections on the machine. > -- > 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 -- 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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