From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4AE80C742D7 for ; Sat, 13 Jul 2019 00:41:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2941B20896 for ; Sat, 13 Jul 2019 00:41:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727826AbfGMAlD (ORCPT ); Fri, 12 Jul 2019 20:41:03 -0400 Received: from charlotte.tuxdriver.com ([70.61.120.58]:41944 "EHLO smtp.tuxdriver.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727489AbfGMAlC (ORCPT ); Fri, 12 Jul 2019 20:41:02 -0400 Received: from cpe-2606-a000-111b-405a-0-0-0-1ff7.dyn6.twc.com ([2606:a000:111b:405a::1ff7] helo=localhost) by smtp.tuxdriver.com with esmtpsa (TLSv1:AES256-SHA:256) (Exim 4.63) (envelope-from ) id 1hm65f-0005t8-9Z; Fri, 12 Jul 2019 20:40:47 -0400 Date: Fri, 12 Jul 2019 20:40:11 -0400 From: Neil Horman To: Toke =?iso-8859-1?Q?H=F8iland-J=F8rgensen?= Cc: Ido Schimmel , David Miller , netdev@vger.kernel.org, jiri@mellanox.com, mlxsw@mellanox.com, dsahern@gmail.com, roopa@cumulusnetworks.com, nikolay@cumulusnetworks.com, andy@greyhouse.net, pablo@netfilter.org, jakub.kicinski@netronome.com, pieter.jansenvanvuuren@netronome.com, andrew@lunn.ch, f.fainelli@gmail.com, vivien.didelot@gmail.com, idosch@mellanox.com Subject: Re: [PATCH net-next 00/11] Add drop monitor for offloaded data paths Message-ID: <20190713004011.GA24036@localhost.localdomain> References: <20190707075828.3315-1-idosch@idosch.org> <20190707.124541.451040901050013496.davem@davemloft.net> <20190711123909.GA10978@splinter> <20190711235354.GA30396@hmswarspite.think-freely.org> <87r26vvbz8.fsf@toke.dk> <20190712121859.GB13696@hmswarspite.think-freely.org> <871ryvv3dy.fsf@toke.dk> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <871ryvv3dy.fsf@toke.dk> User-Agent: Mutt/1.12.0 (2019-05-25) Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Fri, Jul 12, 2019 at 02:33:29PM +0200, Toke Høiland-Jørgensen wrote: > Neil Horman writes: > > > On Fri, Jul 12, 2019 at 11:27:55AM +0200, Toke Høiland-Jørgensen wrote: > >> Neil Horman writes: > >> > >> > On Thu, Jul 11, 2019 at 03:39:09PM +0300, Ido Schimmel wrote: > >> >> On Sun, Jul 07, 2019 at 12:45:41PM -0700, David Miller wrote: > >> >> > From: Ido Schimmel > >> >> > Date: Sun, 7 Jul 2019 10:58:17 +0300 > >> >> > > >> >> > > Users have several ways to debug the kernel and understand why a packet > >> >> > > was dropped. For example, using "drop monitor" and "perf". Both > >> >> > > utilities trace kfree_skb(), which is the function called when a packet > >> >> > > is freed as part of a failure. The information provided by these tools > >> >> > > is invaluable when trying to understand the cause of a packet loss. > >> >> > > > >> >> > > In recent years, large portions of the kernel data path were offloaded > >> >> > > to capable devices. Today, it is possible to perform L2 and L3 > >> >> > > forwarding in hardware, as well as tunneling (IP-in-IP and VXLAN). > >> >> > > Different TC classifiers and actions are also offloaded to capable > >> >> > > devices, at both ingress and egress. > >> >> > > > >> >> > > However, when the data path is offloaded it is not possible to achieve > >> >> > > the same level of introspection as tools such "perf" and "drop monitor" > >> >> > > become irrelevant. > >> >> > > > >> >> > > This patchset aims to solve this by allowing users to monitor packets > >> >> > > that the underlying device decided to drop along with relevant metadata > >> >> > > such as the drop reason and ingress port. > >> >> > > >> >> > We are now going to have 5 or so ways to capture packets passing through > >> >> > the system, this is nonsense. > >> >> > > >> >> > AF_PACKET, kfree_skb drop monitor, perf, XDP perf events, and now this > >> >> > devlink thing. > >> >> > > >> >> > This is insanity, too many ways to do the same thing and therefore the > >> >> > worst possible user experience. > >> >> > > >> >> > Pick _ONE_ method to trap packets and forward normal kfree_skb events, > >> >> > XDP perf events, and these taps there too. > >> >> > > >> >> > I mean really, think about it from the average user's perspective. To > >> >> > see all drops/pkts I have to attach a kfree_skb tracepoint, and not just > >> >> > listen on devlink but configure a special tap thing beforehand and then > >> >> > if someone is using XDP I gotta setup another perf event buffer capture > >> >> > thing too. > >> >> > >> >> Dave, > >> >> > >> >> Before I start working on v2, I would like to get your feedback on the > >> >> high level plan. Also adding Neil who is the maintainer of drop_monitor > >> >> (and counterpart DropWatch tool [1]). > >> >> > >> >> IIUC, the problem you point out is that users need to use different > >> >> tools to monitor packet drops based on where these drops occur > >> >> (SW/HW/XDP). > >> >> > >> >> Therefore, my plan is to extend the existing drop_monitor netlink > >> >> channel to also cover HW drops. I will add a new message type and a new > >> >> multicast group for HW drops and encode in the message what is currently > >> >> encoded in the devlink events. > >> >> > >> > A few things here: > >> > IIRC we don't announce individual hardware drops, drivers record them in > >> > internal structures, and they are retrieved on demand via ethtool calls, so you > >> > will either need to include some polling (probably not a very performant idea), > >> > or some sort of flagging mechanism to indicate that on the next message sent to > >> > user space you should go retrieve hw stats from a given interface. I certainly > >> > wouldn't mind seeing this happen, but its more work than just adding a new > >> > netlink message. > >> > > >> > Also, regarding XDP drops, we wont see them if the xdp program is offloaded to > >> > hardware (you'll need your hw drop gathering mechanism for that), but for xdp > >> > programs run on the cpu, dropwatch should alrady catch those. I.e. if the xdp > >> > program returns a DROP result for a packet being processed, the OS will call > >> > kfree_skb on its behalf, and dropwatch wil call that. > >> > >> There is no skb by the time an XDP program runs, so this is not true. As > >> I mentioned upthread, there's a tracepoint that will get called if an > >> error occurs (or the program returns XDP_ABORTED), but in most cases, > >> XDP_DROP just means that the packet silently disappears... > >> > > As I noted, thats only true for xdp programs that are offloaded to hardware, I > > was only speaking for XDP programs that run on the cpu. For the former case, we > > obviously need some other mechanism to detect drops, but for cpu executed xdp > > programs, the OS is responsible for freeing skbs associated with programs the > > return XDP_DROP. > > Ah, I think maybe you're thinking of generic XDP (also referred to as > skb mode)? That is a separate mode; an XDP program loaded in "native Yes, was I not clear about that? Neil > mode" (or "driver mode") runs on the CPU, but before the skb is created; > this is the common case for XDP, and there is no skb and thus no drop > notification in this mode. > > There is *also* an offload mode for XDP programs, but that is only > supported by netronome cards thus far, so not as commonly used... > > -Toke >