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=-16.5 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,USER_AGENT_GIT 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 BC859C433DB for ; Thu, 4 Feb 2021 16:49:36 +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 42A3A64DF5 for ; Thu, 4 Feb 2021 16:49:36 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 42A3A64DF5 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=daynix.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:60696 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1l7hp1-00038S-75 for qemu-devel@archiver.kernel.org; Thu, 04 Feb 2021 11:49:35 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:39010) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1l7hbo-00037Y-02 for qemu-devel@nongnu.org; Thu, 04 Feb 2021 11:35:56 -0500 Received: from mail-lj1-x235.google.com ([2a00:1450:4864:20::235]:34969) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.90_1) (envelope-from ) id 1l7hbm-0002VA-3U for qemu-devel@nongnu.org; Thu, 04 Feb 2021 11:35:55 -0500 Received: by mail-lj1-x235.google.com with SMTP id a17so4177292ljq.2 for ; Thu, 04 Feb 2021 08:35:53 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=daynix-com.20150623.gappssmtp.com; s=20150623; h=from:to:cc:subject:date:message-id:in-reply-to:references :mime-version:content-transfer-encoding; bh=wFTDn18MKEjEreyR/iIK0LARtIm3Uw+Kz3Ig8TxkhcU=; b=fsUodhfNUiJfS4dKHar7UOt66uUXcIZyOggyXW6NXs+Uv5XW5/rlX/dbtpiEbcrkHw EbUx7crCL3kEk4PulypAyuRsZozI4NWUS/0cWR0iIZ8gIH00miQSSfrcHROkGulHTu+A Azy9fL0HgCVGtDVJDtgJgjgvoqZXZ1XNITQ6XQ7dxzPe+iDLD0IcU4F8un8MKbQxYArz aET9C8tyi0+zMoWghPjfAelAkngYLiiiC+zdplyepkTCFYbvio+1QmILwZCLcZOZvDPK 5sf2lZg0/C67lQ7nHAPUNfBrS5TYUE9Rzww0XddXjBgE8tlfAfgxeN6jorU4GCRx8WBG kCtQ== 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:date:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=wFTDn18MKEjEreyR/iIK0LARtIm3Uw+Kz3Ig8TxkhcU=; b=pVY74g19HXy42wSAUFnm/Yvlmt7CIJJfBIGarJwjf8ENaUTqFJz2qP9s0j5/1R9xnH ZtDaStptdK2Au6n/TnWB5HWk6kZBqgmEOi8DZ7UiLJwhtVmIamff98zZszaR7sIYRKwA 3J68sbqTYCQSzY36+kJxB8mI34KHdal/xK2Jh0UR9k40XJMquBjEKPtRZVLQhF/NIM/Q qCjkRdKlVBFjGG3FzoGRMujFRnCLUoUBM2UHgRfvWZ/jZ2mpzJfW+nerUfpqnt3MK5l+ pWcZNgO+uOnazOdtMJdiGvQeN1ULziEhI/ru0qjGZRPW0JdYXZz2zAp7B9VVcTtT2tJT AMjg== X-Gm-Message-State: AOAM532k3f+OHGzFb43qshZDc2e5coem5++WR2eaU1c+5J/+bftPTYYZ mkXH13GTf0SJH9aWe36ZX/5T8A== X-Google-Smtp-Source: ABdhPJy7jgadNcQcMVGMkDPvvXvamB9+X2JSXXqWWDDsbW6vyW3WZiNinRdKOkiALGHwDSn7Rwr8rQ== X-Received: by 2002:a2e:1519:: with SMTP id s25mr109231ljd.495.1612456551012; Thu, 04 Feb 2021 08:35:51 -0800 (PST) Received: from navi.cosmonova.net.ua ([95.67.24.131]) by smtp.gmail.com with ESMTPSA id c123sm668172lfd.95.2021.02.04.08.35.49 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 04 Feb 2021 08:35:50 -0800 (PST) From: Andrew Melnychenko To: jasowang@redhat.com, mst@redhat.com Subject: [RFC PATCH v4 6/7] docs: Added eBPF documentation. Date: Thu, 4 Feb 2021 19:09:50 +0200 Message-Id: <20210204170951.91805-7-andrew@daynix.com> X-Mailer: git-send-email 2.30.0 In-Reply-To: <20210204170951.91805-1-andrew@daynix.com> References: <20210204170951.91805-1-andrew@daynix.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Received-SPF: none client-ip=2a00:1450:4864:20::235; envelope-from=andrew@daynix.com; helo=mail-lj1-x235.google.com X-Spam_score_int: -18 X-Spam_score: -1.9 X-Spam_bar: - X-Spam_report: (-1.9 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_NONE=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@daynix.com, yuri.benditovich@daynix.com, berrange@redhat.com, qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" From: Andrew Signed-off-by: Yuri Benditovich Signed-off-by: Andrew Melnychenko --- docs/ebpf_rss.rst | 125 ++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 125 insertions(+) create mode 100644 docs/ebpf_rss.rst diff --git a/docs/ebpf_rss.rst b/docs/ebpf_rss.rst new file mode 100644 index 0000000000..5beecfe33f --- /dev/null +++ b/docs/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 'linuxhdrs' in Makefile.ebpf to reflect the location of the kernel source tree + + $ cd 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 tun_rss_steering.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. -- 2.30.0