From mboxrd@z Thu Jan 1 00:00:00 1970 From: Benjamin LaHaise Subject: Re: PPPoE performance regression Date: Wed, 13 Jun 2012 11:55:41 -0400 Message-ID: <20120613155541.GD2361@kvack.org> References: <1339143949.24571.72.camel@dualcore.traverse> <1339144110.13998.1.camel@i7.infradead.org> <1339144954.24571.80.camel@dualcore.traverse> <1339147045.13998.3.camel@i7.infradead.org> <1339289425.2661.27.camel@laptop> <1339317136.2851.54.camel@shinybook.infradead.org> <1339581421.11011.18.camel@shinybook.infradead.org> <1339595401.11011.48.camel@shinybook.infradead.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Nathan Williams , Karl Hiramoto , "David S. Miller" , netdev@vger.kernel.org, Paul Mackerras , John Crispin To: David Woodhouse Return-path: Received: from kanga.kvack.org ([205.233.56.17]:56793 "EHLO kanga.kvack.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751324Ab2FMPzm (ORCPT ); Wed, 13 Jun 2012 11:55:42 -0400 Content-Disposition: inline In-Reply-To: <1339595401.11011.48.camel@shinybook.infradead.org> Sender: netdev-owner@vger.kernel.org List-ID: On Wed, Jun 13, 2012 at 02:50:01PM +0100, David Woodhouse wrote: > On Wed, 2012-06-13 at 10:57 +0100, David Woodhouse wrote: > > This doesn't look *so* evil... if the basic concept of using > > skb_orphan() and then setting our own destructor is OK, then I'll work > > out the rest of the details and do it for l2tp too. > > Stupid dwmw2. With patch this time... Does this actually work? Could the skb not end up sitting on the receive queue of a user socket indefinitely, deferring all further transmits? From an ISP point of view, PPPoE and L2TP are most typically used on links where the congestion point is not the local interface the packets are being pumped into (think of the vast majority of ethernet based DSL modems), and this kind of transmit overhead is a pure waste of CPU cycles. The only solution that generically works in most PPPoE/L2TP situations is to shape outgoing traffic to the speed of limiting link. Maybe there's a PPP extension that does flow control... -ben