From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Miller Subject: Re: [PATCH 0/2] Get rid of ndo_xmit_flush Date: Wed, 27 Aug 2014 13:46:50 -0700 (PDT) Message-ID: <20140827.134650.1202884223919773168.davem@davemloft.net> References: <20140825.163458.1117073971092495452.davem@davemloft.net> <1409142672.26515.24.camel@localhost> <1409145838.3173.41.camel@edumazet-glaptop2.roam.corp.google.com> Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Cc: hannes@stressinduktion.org, netdev@vger.kernel.org, therbert@google.com, jhs@mojatatu.com, edumazet@google.com, jeffrey.t.kirsher@intel.com, rusty@rustcorp.com.au, dborkman@redhat.com, brouer@redhat.com To: eric.dumazet@gmail.com Return-path: Received: from shards.monkeyblade.net ([149.20.54.216]:40226 "EHLO shards.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S964892AbaH0Uqv (ORCPT ); Wed, 27 Aug 2014 16:46:51 -0400 In-Reply-To: <1409145838.3173.41.camel@edumazet-glaptop2.roam.corp.google.com> Sender: netdev-owner@vger.kernel.org List-ID: From: Eric Dumazet Date: Wed, 27 Aug 2014 06:23:58 -0700 > On Wed, 2014-08-27 at 14:31 +0200, Hannes Frederic Sowa wrote: > >> One thing one should keep in mind is, that there must be a skb available >> to trigger the flush, maybe this will hurt us one day. >> >> Thinking more about it should we go with a coccinelle script and >> replace/extend ndo_start_xmit with an additional argument? > > This will be a pain for backports and things like that. Agreed. > skb->xmit_more is a bit annoying, because it consumes one bit in all > skbs, while it could be one byte per cpu as ndo_start_xmit() is called > while BH are disabled. > > It also forces a cache line dirtying, that will hurt qdisc like HTB > where skbs can be cooked/enqueued by remote cpus. The xmit_more value sits in the same cache line as the queue number, which also gets dirtied in the TX fast path.