From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jesper Dangaard Brouer Subject: Re: [PATCH 0/2] Get rid of ndo_xmit_flush Date: Wed, 27 Aug 2014 14:19:18 +0200 Message-ID: <20140827141918.198cba38@redhat.com> References: <20140825.163458.1117073971092495452.davem@davemloft.net> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Cc: netdev@vger.kernel.org, therbert@google.com, jhs@mojatatu.com, hannes@stressinduktion.org, edumazet@google.com, jeffrey.t.kirsher@intel.com, rusty@rustcorp.com.au, dborkman@redhat.com, brouer@redhat.com To: David Miller Return-path: Received: from mx1.redhat.com ([209.132.183.28]:49094 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755814AbaH0MTd (ORCPT ); Wed, 27 Aug 2014 08:19:33 -0400 In-Reply-To: <20140825.163458.1117073971092495452.davem@davemloft.net> Sender: netdev-owner@vger.kernel.org List-ID: On Mon, 25 Aug 2014 16:34:58 -0700 (PDT) David Miller wrote: > Given Jesper's performance numbers, it's not the way to go. > > Instead, go with a signalling scheme via new boolean skb->xmit_more. > > This has several advantages: > > 1) Nearly trivial driver support, just protect the tail pointer > update with the skb->xmit_more check. > > 2) No extra indirect calls in the non-deferral cases. Even-though it is obvious that this new API skb->xmit_more will not hurt performance, especially given skb->xmit_more is always 0 in this kernel, I've still run my pktgen performance tests. Compared to baseline[1]: (averaged 5609929 pps) (details below signature) * (1/5609929*10^9)-(1/5603728*10^9) = -0.197ns As expected, this API does not hurt performance (as -0.197ns is below our accuracy levels). [1] http://thread.gmane.org/gmane.linux.network/327254/focus=327838 -- Best regards, Jesper Dangaard Brouer MSc.CS, Sr. Network Kernel Developer at Red Hat Author of http://www.iptv-analyzer.org LinkedIn: http://www.linkedin.com/in/brouer Results: on branch bulking02 ---------------------------- Kernel with skb->xmit_more API. Kernel at: * commit a3d1214688d ("neigh: document gc_thresh2") With no HT: * ethtool -C eth5 rx-usecs 30 * tuned-adm profile latency-performance Results (pktgen): * instant rx:1 tx:5604056 pps n:250 average: rx:1 tx:5604013 pps (instant variation TX 0.001 ns (min:-0.114 max:0.104) RX 0.000 ns) * instant rx:1 tx:5603388 pps n:87 average: rx:1 tx:5603872 pps (instant variation TX -0.015 ns (min:-0.031 max:0.060) RX 0.000 ns) * instant rx:1 tx:5604332 pps n:429 average: rx:1 tx:5603300 pps (instant variation TX 0.033 ns (min:-0.094 max:0.881) RX 0.000 ns) * Average: (5604013+5603872+5603300)/3 = 5603728 Compared to baseline: (averaged 5609929 pps) * (1/5609929*10^9)-(1/5603728*10^9) = -0.197ns