From mboxrd@z Thu Jan 1 00:00:00 1970 From: Florian Westphal Subject: Re: [net-next PATCH v1 1/3] net: sched: af_packet support for direct ring access Date: Mon, 6 Oct 2014 02:29:51 +0200 Message-ID: <20141006002951.GA24376@breakpoint.cc> References: <20141006000629.32055.2295.stgit@nitbit.x32> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: dborkman@redhat.com, fw@strlen.de, gerlitz.or@gmail.com, hannes@stressinduktion.org, netdev@vger.kernel.org, john.ronciak@intel.com, amirv@mellanox.com, eric.dumazet@gmail.com, danny.zhou@intel.com To: John Fastabend Return-path: Received: from Chamillionaire.breakpoint.cc ([80.244.247.6]:45051 "EHLO Chamillionaire.breakpoint.cc" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751775AbaJFA36 (ORCPT ); Sun, 5 Oct 2014 20:29:58 -0400 Content-Disposition: inline In-Reply-To: <20141006000629.32055.2295.stgit@nitbit.x32> Sender: netdev-owner@vger.kernel.org List-ID: John Fastabend wrote: > There is one critical difference when running with these interfaces > vs running without them. In the normal case the af_packet module > uses a standard descriptor format exported by the af_packet user > space headers. In this model because we are working directly with > driver queues the descriptor format maps to the descriptor format > used by the device. User space applications can learn device > information from the socket option PACKET_DEV_DESC_INFO which > should provide enough details to extrapulate the descriptor formats. > Although this adds some complexity to user space it removes the > requirement to copy descriptor fields around. I find it very disappointing that we seem to have to expose such hardware specific details to userspace via hw-independent interface. How big of a cost are we talking about when you say that it 'removes the requirement to copy descriptor fields'? Thanks, Florian