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=-5.4 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, 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 E5315C2D0A3 for ; Wed, 4 Nov 2020 02:16:01 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 3D8942071A for ; Wed, 4 Nov 2020 02:16:01 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="RvOQCG50" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 3D8942071A Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:46552 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1ka8LA-0002ev-5R for qemu-devel@archiver.kernel.org; Tue, 03 Nov 2020 21:16:00 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:51588) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1ka8KU-0002DD-7V for qemu-devel@nongnu.org; Tue, 03 Nov 2020 21:15:18 -0500 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:30846) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1ka8KS-0007zR-BD for qemu-devel@nongnu.org; Tue, 03 Nov 2020 21:15:17 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1604456115; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=QcCelvENtzzTasIe59XfnvMhSV6K5TB1bs4yMVPMv+Y=; b=RvOQCG508wkYaF5aDZ+avJPKh8A96LfbDjwxRnWKmaNbjBtKBD4go+jf/G+M4h67Wylba6 ijvd+zXQ26whkPd5kvUUWB8fUQN30vqFDhSUsiW10yjqTPKMdA+JduJd1obynwz/ZTqKW2 BX7QaYWg1hq3jDpLBiXwbCjm1WjNiMk= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-27-iVn9CxWsO92y29etiaiW7A-1; Tue, 03 Nov 2020 21:15:13 -0500 X-MC-Unique: iVn9CxWsO92y29etiaiW7A-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id C90415F9D1; Wed, 4 Nov 2020 02:15:11 +0000 (UTC) Received: from [10.72.13.133] (ovpn-13-133.pek2.redhat.com [10.72.13.133]) by smtp.corp.redhat.com (Postfix) with ESMTP id 82FCA5C1D0; Wed, 4 Nov 2020 02:15:06 +0000 (UTC) Subject: Re: [RFC PATCH 0/6] eBPF RSS support for virtio-net To: =?UTF-8?Q?Daniel_P=2e_Berrang=c3=a9?= , Yuri Benditovich References: <20201102185115.7425-1-andrew@daynix.com> <0164a42f-4542-6f3e-bd71-3319dfaae190@redhat.com> <20201103115602.GI205187@redhat.com> From: Jason Wang Message-ID: Date: Wed, 4 Nov 2020 10:15:05 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <20201103115602.GI205187@redhat.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=jasowang@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US Received-SPF: pass client-ip=216.205.24.124; envelope-from=jasowang@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/11/03 00:03:41 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Yan Vugenfirer , Andrew Melnychenko , qemu-devel@nongnu.org, "Michael S . Tsirkin" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 2020/11/3 下午7:56, Daniel P. Berrangé wrote: > On Tue, Nov 03, 2020 at 12:32:43PM +0200, Yuri Benditovich wrote: >> On Tue, Nov 3, 2020 at 11:02 AM Jason Wang wrote: >> >>> On 2020/11/3 上午2:51, Andrew Melnychenko wrote: >>>> Basic idea is to use eBPF to calculate and steer packets in TAP. >>>> RSS(Receive Side Scaling) is used to distribute network packets to guest >>> virtqueues >>>> by calculating packet hash. >>>> eBPF RSS allows us to use RSS with vhost TAP. >>>> >>>> This set of patches introduces the usage of eBPF for packet steering >>>> and RSS hash calculation: >>>> * RSS(Receive Side Scaling) is used to distribute network packets to >>>> guest virtqueues by calculating packet hash >>>> * eBPF RSS suppose to be faster than already existing 'software' >>>> implementation in QEMU >>>> * Additionally adding support for the usage of RSS with vhost >>>> >>>> Supported kernels: 5.8+ >>>> >>>> Implementation notes: >>>> Linux TAP TUNSETSTEERINGEBPF ioctl was used to set the eBPF program. >>>> Added eBPF support to qemu directly through a system call, see the >>>> bpf(2) for details. >>>> The eBPF program is part of the qemu and presented as an array of bpf >>>> instructions. >>>> The program can be recompiled by provided Makefile.ebpf(need to adjust >>>> 'linuxhdrs'), >>>> although it's not required to build QEMU with eBPF support. >>>> Added changes to virtio-net and vhost, primary eBPF RSS is used. >>>> 'Software' RSS used in the case of hash population and as a fallback >>> option. >>>> For vhost, the hash population feature is not reported to the guest. >>>> >>>> Please also see the documentation in PATCH 6/6. >>>> >>>> I am sending those patches as RFC to initiate the discussions and get >>>> feedback on the following points: >>>> * Fallback when eBPF is not supported by the kernel >>> >>> Yes, and it could also a lacking of CAP_BPF. >>> >>> >>>> * Live migration to the kernel that doesn't have eBPF support >>> >>> Is there anything that we needs special treatment here? >>> >>> Possible case: rss=on, vhost=on, source system with kernel 5.8 (everything >> works) -> dest. system 5.6 (bpf does not work), the adapter functions, but >> all the steering does not use proper queues. >> >> >> >> >>>> * Integration with current QEMU build >>> >>> Yes, a question here: >>> >>> 1) Any reason for not using libbpf, e.g it has been shipped with some >>> distros >>> >> We intentionally do not use libbpf, as it present only on some distros. >> We can switch to libbpf, but this will disable bpf if libbpf is not >> installed > If we were modifying existing funtionality then introducing a dep on > libbpf would be a problem as you'd be breaking existing QEMU users > on distros without libbpf. > > This is brand new functionality though, so it is fine to place a > requirement on libbpf. If distros don't ship that library and they > want BPF features in QEMU, then those distros should take responsibility > for adding libbpf to their package set. > >>> 2) It would be better if we can avoid shipping bytecodes >>> >> >> This creates new dependencies: llvm + clang + ... >> We would prefer byte code and ability to generate it if prerequisites are >> installed. > I've double checked with Fedora, and generating the BPF program from > source is a mandatory requirement for QEMU. Pre-generated BPF bytecode > is not permitted. > > There was also a question raised about the kernel ABI compatibility > for BPF programs ? > > https://lwn.net/Articles/831402/ > > "The basic problem is that when BPF is compiled, it uses a set > of kernel headers that describe various kernel data structures > for that particular version, which may be different from those > on the kernel where the program is run. Until relatively recently, > that was solved by distributing the BPF as C code along with the > Clang compiler to build the BPF on the system where it was going > to be run." > > Is this not an issue for QEMU's usage of BPF here ? That's good point. Actually, DPDK ships RSS bytecodes but I don't know it works. But as mentioned in the link, if we generate the code with BTF that would be fine. Thanks > > The dependancy on llvm is unfortunate for people who build with GCC, > but at least they can opt-out via a configure switch if they really > want to. As that LWN article notes, GCC will gain BPF support > > > Regards, > Daniel