From mboxrd@z Thu Jan 1 00:00:00 1970 From: Rick Jones Subject: Re: [PATCH NEXT 0/2] qlcnic: Add Qlogic 1/10Gb Ethernet driver for CNA devices Date: Tue, 05 Jan 2010 17:33:38 -0800 Message-ID: <4B43E872.5000809@hp.com> References: <7608421F3572AB4292BB2532AE89D5658B0BAE9450@AVEXMB1.qlogic.org> <20100105.154928.80012641.davem@davemloft.net> <7608421F3572AB4292BB2532AE89D5658B0BAE9471@AVEXMB1.qlogic.org> <20100105.163343.14826539.davem@davemloft.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Cc: dhananjay.phadke@qlogic.com, shemminger@vyatta.com, amit.salecha@qlogic.com, netdev@vger.kernel.org To: David Miller Return-path: Received: from g5t0008.atlanta.hp.com ([15.192.0.45]:25468 "EHLO g5t0008.atlanta.hp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753978Ab0AFBdl (ORCPT ); Tue, 5 Jan 2010 20:33:41 -0500 In-Reply-To: <20100105.163343.14826539.davem@davemloft.net> Sender: netdev-owner@vger.kernel.org List-ID: David Miller wrote: > From: Dhananjay Phadke > 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@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html