From patchwork Tue Jun 25 09:48:51 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Wencheng Yang X-Patchwork-Id: 13710807 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org 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 smtp.lore.kernel.org (Postfix) with ESMTPS id 1D586C41513 for ; Tue, 25 Jun 2024 09:49:40 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1sM2nU-0007jb-Pz; Tue, 25 Jun 2024 05:49:08 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1sM2nT-0007iq-B3; Tue, 25 Jun 2024 05:49:07 -0400 Received: from mail-oo1-xc33.google.com ([2607:f8b0:4864:20::c33]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.90_1) (envelope-from ) id 1sM2nR-0003Fe-I2; Tue, 25 Jun 2024 05:49:07 -0400 Received: by mail-oo1-xc33.google.com with SMTP id 006d021491bc7-5c2177bf7a8so102088eaf.2; Tue, 25 Jun 2024 02:49:04 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1719308943; x=1719913743; darn=nongnu.org; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:from:to:cc:subject:date:message-id:reply-to; bh=ScpTwYEgj3XP1Q2imqxoItyBRdYB3AJf+gJpu+LZmxg=; b=McK/1NZt4R+SctpChBrf/NBWTcSESz5xcnbOzd7wE7CNDyYJr7zp65rj5oL5o0CqIe Fjul8d7lsL4j7jxrSNI37k72AnxvSiSCHZ1O3+v91c/rvyHC4Ck9P/Kh39f4nk2i/opK plbpNMHBxO1vSRORHAZ1IZwn8X3r7KDHJiVShDkvw0gc+VIhdr/e+kFm6fRcKbTo1MTr eKCl1h+qbX37o6yPP4L0z/TEND7bmTda82JsNkSuCeYg1KwpyuuIDDrvphNAXvuEkuS/ Nwwhfsr+Wc6LmENM/XpkSJXVov8Yo9ix6H2mBRPV7Qg2MuwkMDItO2JAImtjl+tsdt7z Yocw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1719308943; x=1719913743; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=ScpTwYEgj3XP1Q2imqxoItyBRdYB3AJf+gJpu+LZmxg=; b=xTiuegUzQqYJs+X1g/+yYmFZfiahvCgmC5fQprfMGbRcVwspuaYKq9FeFaH1fJOtkF tdwb8sbtRnY88IrbrjAtdSmj5gGy2h/Yz84crKM0BrLmaDqElDx9DVoRgJFrF8i9bWk6 tVTa5OFDZdhAHth5vPZZzAz1b7Ehh87WQmQw2AzsifUqZVt8sAXoeZ1EHSXCD52ZSsMH /0atd+P33FZANQ8I+7dt4vp0GjpSG8+Q1vB379vUbdPr6ZW0BgtBDnCB2+k1dJW88Ldl Lb9BVM29hdnjqFH1RTA3BH6zMESJDJme9atFfw6GbEUFuaKNLJ2AAAQA03Os0aKipnGg OAZQ== X-Forwarded-Encrypted: i=1; AJvYcCWNS/6zxYv9gw5e6ShJqadspu/j0rXMQXfB0qICfyPW9XktVln8O6YCylpHgwwlcZZFIknGLWl9CpF+iOS1ncFqwW6iiXBT X-Gm-Message-State: AOJu0YwX+82Wd7Yug60nPUN8dMfIvbJnslGl8zUdd5dOx2H2J92QxFd4 62Dd/YeDqi1oTgV82ydOOslMc7GWzR4ukpewQWwvJEyI196fHwsXgpRtgwVP4+o= X-Google-Smtp-Source: AGHT+IG+NAHBxlhvrocSQH+QlSRJ/ve3AiLibaLODN+W/a9pusNx8K2d+xmAeWAyX7N5mSMeJgyLkw== X-Received: by 2002:a05:6870:1602:b0:259:8c82:999 with SMTP id 586e51a60fabf-25d06cd3dc7mr8321740fac.25.1719308942746; Tue, 25 Jun 2024 02:49:02 -0700 (PDT) Received: from localhost.localdomain ([118.242.3.34]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-70672e24d7asm4784363b3a.114.2024.06.25.02.49.00 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 25 Jun 2024 02:49:02 -0700 (PDT) From: Wencheng Yang To: qemu-devel@nongnu.org Cc: mst@redhat.com, jasowang@redhat.com, qemu-stable@nongnu.org, thomas Subject: [PATCH v4] virtio-net: Notify the guest with the latest available idx Date: Tue, 25 Jun 2024 17:48:51 +0800 Message-Id: <20240625094851.5252-1-east.moutain.yang@gmail.com> X-Mailer: git-send-email 2.39.0 MIME-Version: 1.0 Received-SPF: pass client-ip=2607:f8b0:4864:20::c33; envelope-from=east.moutain.yang@gmail.com; helo=mail-oo1-xc33.google.com 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, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, FREEMAIL_FROM=0.001, RCVD_IN_DNSWL_NONE=-0.0001, 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: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org From: thomas Patch 06b12970174 ("virtio-net: fix network stall under load") added double-check to test whether the available buffer size can satisfy the request or not, in case the guest has added some buffers to the avail ring simultaneously after the first check. It will be lucky if the available buffer size becomes okay after the double-check, then the host can send the packet to the guest. If the buffer size still can't satisfy the request, even if the guest has added some buffers, notify the guest with the latest available idx seen by the host, similiar to the action taken by the host after the first check, else viritio-net would stall at the host side forever. The case below can reproduce the stall. Guest 0 +--------+ | iperf | ---------------> | server | Host | +--------+ +--------+ | ... | iperf |---- | client |---- Guest n +--------+ | +--------+ | | iperf | ---------------> | server | +--------+ Boot many guests from qemu with virtio network: qemu ... -netdev tap,id=net_x \ -device virtio-net-pci-non-transitional,\ iommu_platform=on,mac=xx:xx:xx:xx:xx:xx,netdev=net_x Each guest acts as iperf server with commands below: iperf3 -s -D -i 10 -p 8001 iperf3 -s -D -i 10 -p 8002 The host as iperf client: iperf3 -c guest_IP -p 8001 -i 30 -w 256k -P 20 -t 40000 iperf3 -c guest_IP -p 8002 -i 30 -w 256k -P 20 -t 40000 After some time, the host loses connection to the guest, the guest can send packet to the host, but can't receive packet from host. It's more likely to happen if SWIOTLB is enabled in the guest, allocating and freeing bounce buffer takes some CPU ticks, copying from/to bounce buffer takes more CPU ticks, compared with that there is no bounce buffer in the guest. Once the rate of producing packets from the host approximates the rate of receiveing packets in the guest, the guest would loop in NAPI. receive packets --- | | v | free buf virtnet_poll | | v | add buf to avail ring --- | | need kick the host? | NAPI continues v receive packets --- | | v | free buf virtnet_poll | | v | add buf to avail ring --- | v ... ... On the other hand, the host fetches free buf from avail ring, if the buf in the avail ring is not enough, the host notifies the guest the event by writing the avail idx read from avail ring to the event idx of used ring, then the host goes to sleep, waiting for the kick signal from the guest. Once the guest finds the host is waiting for kick singal (in virtqueue_kick_prepare_split()), it kicks the host. The host may stall forever at the sequences below: Host Guest ------------ ----------- fetch buf, send packet receive packet --- ... ... | fetch buf, send packet add buf | ... add buf virtnet_poll buf not enough avail idx-> add buf | read avail idx add buf | add buf --- receive packet --- write event idx ... | waiting for kick add buf virtnet_poll ... | --- no more packet, exit NAPI In the first loop of NAPI above, indicated in the range of virtnet_poll above, the host is sending packets while the guest is receiving packets and adding buf. step 1: The buf is not enough, for example, a big packet needs 5 buf, but the available buf count is 3. The host read current avail idx. step 2: The guest adds some buf, then checks whether the host is waiting for kick signal, not at this time. The used ring is not empty, the guest continues the second loop of NAPI. step 3: The host write the avail idx readed from avail ring to used ring as event idx via virtio_queue_set_notification(q->rx_vq, 1). step 4: At the end of the second loop of NAPI, recheck whether kick is needed, as the event idx in the used ring written by the host is beyound the range of kick condition, the guest will not send kick signal to the host. The patch notifies the guest with the latest avail idx seen by the host in the double-check, which increases the probability of hitting kick condition, but logically speaking, it can't resolve the issue. It's kind of optimization agianst patch 06b12970174. Changelog: v4: - Correct spelling mistake in the subject - Describe the issue that virtio-net is blocked at host side v3: - Add virtio-net tag in the subject - Refine commit log v2: - Add SOB tag at the end of the commit message - Place Fixes tag at the end of the commit message v1: - Initial patch Fixes: 06b12970174 ("virtio-net: fix network stall under load") Signed-off-by: Wencheng Yang --- hw/net/virtio-net.c | 1 + 1 file changed, 1 insertion(+) diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c index 9c7e85caea..23c6c8c898 100644 --- a/hw/net/virtio-net.c +++ b/hw/net/virtio-net.c @@ -1654,6 +1654,7 @@ static int virtio_net_has_buffers(VirtIONetQueue *q, int bufsize) if (virtio_queue_empty(q->rx_vq) || (n->mergeable_rx_bufs && !virtqueue_avail_bytes(q->rx_vq, bufsize, 0))) { + virtio_queue_set_notification(q->rx_vq, 1); return 0; } }