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=-13.6 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=ham 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 CFB2AC07E94 for ; Fri, 4 Jun 2021 07:40:59 +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 6420F613BF for ; Fri, 4 Jun 2021 07:40:59 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 6420F613BF 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]:36524 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lp4Ru-0005Db-Jc for qemu-devel@archiver.kernel.org; Fri, 04 Jun 2021 03:40:58 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:49868) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lp4Nl-0004nK-Bb for qemu-devel@nongnu.org; Fri, 04 Jun 2021 03:36:42 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:55129) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lp4Ni-0001bt-EY for qemu-devel@nongnu.org; Fri, 04 Jun 2021 03:36:41 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1622792197; 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=xsgq0gK3Goz9Vn9RytOuDQBHVHCXduRGHRUJFlGFe4U=; b=b6ly3duM3STzFf0MlQJufDgQOnOqhA+HH9+6GQZzKYmBT1dgtFi+FUu8G/PdhegkJBCZDz 6za/N/RstKRc/JEV1toGh3v6XDkKEYr+gBggXiBp0V7lUXbXXyoPaxQ+5bF2wim1571iCv bWELT3MO7PWKV5ZRpiPZYWY3FpEU2sc= 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-389-jfbmwsEqPgm98scZP0l5WA-1; Fri, 04 Jun 2021 03:36:36 -0400 X-MC-Unique: jfbmwsEqPgm98scZP0l5WA-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 03BE28049CC; Fri, 4 Jun 2021 07:36:35 +0000 (UTC) Received: from localhost.localdomain (ovpn-12-212.pek2.redhat.com [10.72.12.212]) by smtp.corp.redhat.com (Postfix) with ESMTP id 2C9C260CC9; Fri, 4 Jun 2021 07:36:32 +0000 (UTC) From: Jason Wang To: qemu-devel@nongnu.org, peter.maydell@linaro.org Subject: [PULL 6/7] docs: Added eBPF documentation. Date: Fri, 4 Jun 2021 15:36:16 +0800 Message-Id: <20210604073617.69622-7-jasowang@redhat.com> In-Reply-To: <20210604073617.69622-1-jasowang@redhat.com> References: <20210604073617.69622-1-jasowang@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 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-Transfer-Encoding: 8bit Content-Type: text/plain; charset="US-ASCII" Received-SPF: pass client-ip=216.205.24.124; envelope-from=jasowang@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -31 X-Spam_score: -3.2 X-Spam_bar: --- X-Spam_report: (-3.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.37, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, 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: Yuri Benditovich , Andrew Melnychenko , Jason Wang Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" From: Andrew Melnychenko Signed-off-by: Yuri Benditovich Signed-off-by: Andrew Melnychenko Signed-off-by: Jason Wang --- docs/devel/ebpf_rss.rst | 125 ++++++++++++++++++++++++++++++++++++++++++++++++ docs/devel/index.rst | 1 + 2 files changed, 126 insertions(+) create mode 100644 docs/devel/ebpf_rss.rst diff --git a/docs/devel/ebpf_rss.rst b/docs/devel/ebpf_rss.rst new file mode 100644 index 0000000..e009625 --- /dev/null +++ b/docs/devel/ebpf_rss.rst @@ -0,0 +1,125 @@ +=========================== +eBPF RSS virtio-net support +=========================== + +RSS(Receive Side Scaling) is used to distribute network packets to guest virtqueues +by calculating packet hash. Usually every queue is processed then by a specific guest CPU core. + +For now there are 2 RSS implementations in qemu: +- 'in-qemu' RSS (functions if qemu receives network packets, i.e. vhost=off) +- eBPF RSS (can function with also with vhost=on) + +eBPF support (CONFIG_EBPF) is enabled by 'configure' script. +To enable eBPF RSS support use './configure --enable-bpf'. + +If steering BPF is not set for kernel's TUN module, the TUN uses automatic selection +of rx virtqueue based on lookup table built according to calculated symmetric hash +of transmitted packets. +If steering BPF is set for TUN the BPF code calculates the hash of packet header and +returns the virtqueue number to place the packet to. + +Simplified decision formula: + +.. code:: C + + queue_index = indirection_table[hash()%] + + +Not for all packets, the hash can/should be calculated. + +Note: currently, eBPF RSS does not support hash reporting. + +eBPF RSS turned on by different combinations of vhost-net, vitrio-net and tap configurations: + +- eBPF is used: + + tap,vhost=off & virtio-net-pci,rss=on,hash=off + +- eBPF is used: + + tap,vhost=on & virtio-net-pci,rss=on,hash=off + +- 'in-qemu' RSS is used: + + tap,vhost=off & virtio-net-pci,rss=on,hash=on + +- eBPF is used, hash population feature is not reported to the guest: + + tap,vhost=on & virtio-net-pci,rss=on,hash=on + +If CONFIG_EBPF is not set then only 'in-qemu' RSS is supported. +Also 'in-qemu' RSS, as a fallback, is used if the eBPF program failed to load or set to TUN. + +RSS eBPF program +---------------- + +RSS program located in ebpf/rss.bpf.skeleton.h generated by bpftool. +So the program is part of the qemu binary. +Initially, the eBPF program was compiled by clang and source code located at tools/ebpf/rss.bpf.c. +Prerequisites to recompile the eBPF program (regenerate ebpf/rss.bpf.skeleton.h): + + llvm, clang, kernel source tree, bpftool + Adjust Makefile.ebpf to reflect the location of the kernel source tree + + $ cd tools/ebpf + $ make -f Makefile.ebpf + +Current eBPF RSS implementation uses 'bounded loops' with 'backward jump instructions' which present in the last kernels. +Overall eBPF RSS works on kernels 5.8+. + +eBPF RSS implementation +----------------------- + +eBPF RSS loading functionality located in ebpf/ebpf_rss.c and ebpf/ebpf_rss.h. + +The `struct EBPFRSSContext` structure that holds 4 file descriptors: + +- ctx - pointer of the libbpf context. +- program_fd - file descriptor of the eBPF RSS program. +- map_configuration - file descriptor of the 'configuration' map. This map contains one element of 'struct EBPFRSSConfig'. This configuration determines eBPF program behavior. +- map_toeplitz_key - file descriptor of the 'Toeplitz key' map. One element of the 40byte key prepared for the hashing algorithm. +- map_indirections_table - 128 elements of queue indexes. + +`struct EBPFRSSConfig` fields: + +- redirect - "boolean" value, should the hash be calculated, on false - `default_queue` would be used as the final decision. +- populate_hash - for now, not used. eBPF RSS doesn't support hash reporting. +- hash_types - binary mask of different hash types. See `VIRTIO_NET_RSS_HASH_TYPE_*` defines. If for packet hash should not be calculated - `default_queue` would be used. +- indirections_len - length of the indirections table, maximum 128. +- default_queue - the queue index that used for packet that shouldn't be hashed. For some packets, the hash can't be calculated(g.e ARP). + +Functions: + +- `ebpf_rss_init()` - sets ctx to NULL, which indicates that EBPFRSSContext is not loaded. +- `ebpf_rss_load()` - creates 3 maps and loads eBPF program from the rss.bpf.skeleton.h. Returns 'true' on success. After that, program_fd can be used to set steering for TAP. +- `ebpf_rss_set_all()` - sets values for eBPF maps. `indirections_table` length is in EBPFRSSConfig. `toeplitz_key` is VIRTIO_NET_RSS_MAX_KEY_SIZE aka 40 bytes array. +- `ebpf_rss_unload()` - close all file descriptors and set ctx to NULL. + +Simplified eBPF RSS workflow: + +.. code:: C + + struct EBPFRSSConfig config; + config.redirect = 1; + config.hash_types = VIRTIO_NET_RSS_HASH_TYPE_UDPv4 | VIRTIO_NET_RSS_HASH_TYPE_TCPv4; + config.indirections_len = VIRTIO_NET_RSS_MAX_TABLE_LEN; + config.default_queue = 0; + + uint16_t table[VIRTIO_NET_RSS_MAX_TABLE_LEN] = {...}; + uint8_t key[VIRTIO_NET_RSS_MAX_KEY_SIZE] = {...}; + + struct EBPFRSSContext ctx; + ebpf_rss_init(&ctx); + ebpf_rss_load(&ctx); + ebpf_rss_set_all(&ctx, &config, table, key); + if (net_client->info->set_steering_ebpf != NULL) { + net_client->info->set_steering_ebpf(net_client, ctx->program_fd); + } + ... + ebpf_unload(&ctx); + + +NetClientState SetSteeringEBPF() +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +For now, `set_steering_ebpf()` method supported by Linux TAP NetClientState. The method requires an eBPF program file descriptor as an argument. diff --git a/docs/devel/index.rst b/docs/devel/index.rst index cbdbb90..791925d 100644 --- a/docs/devel/index.rst +++ b/docs/devel/index.rst @@ -43,3 +43,4 @@ Contents: qom block-coroutine-wrapper multi-process + ebpf_rss -- 2.7.4