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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 8E292C742B9 for ; Fri, 12 Jul 2019 12:36:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 637202166E for ; Fri, 12 Jul 2019 12:36:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729094AbfGLMde convert rfc822-to-8bit (ORCPT ); Fri, 12 Jul 2019 08:33:34 -0400 Received: from mail-ed1-f65.google.com ([209.85.208.65]:33210 "EHLO mail-ed1-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728778AbfGLMdc (ORCPT ); Fri, 12 Jul 2019 08:33:32 -0400 Received: by mail-ed1-f65.google.com with SMTP id i11so9078821edq.0 for ; Fri, 12 Jul 2019 05:33:31 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:in-reply-to:references:date :message-id:mime-version:content-transfer-encoding; bh=HjuGw6p7lOt//1N6Rn/Ou8xJIhE+xVq2Pi8nDwn2224=; b=pLMzzoxAHjDskWNknsFnI2mVjSgdDIMVNz4lBU6/AnDEFdNrZDLZYFq17tjuWvfr+s +a2ePsulBgvFyILYnAIiHVj/6C0lT5cz4EoJwJrldqJ4YEOtAmmkM93EOQZmqn2e6FFn vWPiaADvIg4kgPjDTj3W91M9hXRoRNkBjwKyv4AVwyi+8fg00rI/FY77Ua9HAxzOJKRj fGeDiZSWGfJ0H1CsxhI4oEDNSAIwIp+oN6d1KsMwMMeAUGj/LcgBTRZfZ+/Q7sB/433D rXlka83Q1mrutoRDIAbJwDIh5AiDhGj7xrL0GhC2anj5FTQNd6xAivC4Dc0XLJWReVK9 4/zA== X-Gm-Message-State: APjAAAUq771g+vR2igRmcZAbP+k6NKTRJWz2DRjCedJMfnwUQHDA9kN7 wrAyBBl997waAC6kYfxR1zc03Q== X-Google-Smtp-Source: APXvYqxo96OoWGr/8JpQOeXT1XLyUSZ44RBcvmfQvKzlalgp3t1ctWVCB6/nqZMW9/q48XRaI1sSfQ== X-Received: by 2002:a05:6402:896:: with SMTP id e22mr4992205edy.202.1562934810700; Fri, 12 Jul 2019 05:33:30 -0700 (PDT) Received: from alrua-x1.borgediget.toke.dk (borgediget.toke.dk. [85.204.121.218]) by smtp.gmail.com with ESMTPSA id g11sm1779183ejm.86.2019.07.12.05.33.29 (version=TLS1_3 cipher=AEAD-AES256-GCM-SHA384 bits=256/256); Fri, 12 Jul 2019 05:33:29 -0700 (PDT) Received: by alrua-x1.borgediget.toke.dk (Postfix, from userid 1000) id 5CE68181CE6; Fri, 12 Jul 2019 14:33:29 +0200 (CEST) From: Toke =?utf-8?Q?H=C3=B8iland-J=C3=B8rgensen?= To: Neil Horman 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 In-Reply-To: <20190712121859.GB13696@hmswarspite.think-freely.org> 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> X-Clacks-Overhead: GNU Terry Pratchett Date: Fri, 12 Jul 2019 14:33:29 +0200 Message-ID: <871ryvv3dy.fsf@toke.dk> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8BIT Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org 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 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