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Mon, 16 Dec 2024 21:45:08 -0800 (PST) Received: from [192.168.1.18] ([223.233.80.80]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-72918ac53f3sm5960772b3a.27.2024.12.16.21.45.06 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 16 Dec 2024 21:45:07 -0800 (PST) Message-ID: Date: Tue, 17 Dec 2024 11:15:03 +0530 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC v4 0/5] Add packed virtqueue to shadow virtqueue To: Eugenio Perez Martin Cc: sgarzare@redhat.com, mst@redhat.com, qemu-devel@nongnu.org, Sahil Siddiq References: <20241205203430.76251-1-sahilcdq@proton.me> Content-Language: en-US From: Sahil Siddiq Autocrypt: addr=icegambit91@gmail.com; keydata= xsDNBGcgaYEBDADpKUSKbchLCMdCuZGkuF50/7BiraKc8Ch+mk4T+2+E2/6qXAkalvCkFoqx 3/sa35rconZAFzB/r19e7i3UajIQjATvENrGxqe/IFqcJxo2Jr1HQBwCrsmlQoUCilSC6nDi ejcEIAFytJORDkCcZwLXPjdf5/4pbqVAW5823LB5j5F0TqHAnGY1RhS2V1eBPdRqjAA3xecT zTmLHlkqAXgM2DOot1KbycedZSieCwEykTXMaLC0/3Gyo2Cp1WTWOIyD0hsXpLyFioV4FaX2 Lm+z45Zc4PoNXeC6+l4PdDxixs+saAbadknP+9omwlb+PkMd3esq2wkowTwTJVJK8FCCNTo5 2OArA/ddxcyXY25JHN7vzGooFNW6Bb9YV+lbX6y95ytE3KcAmid73tQrcjlebIpgNAvOMyyZ BgQJY0HSu3DGNZuKtbNM3iTl82TFj7MVgkEffgF83N6XyBqDztIz2lN47/q5wyRi3jda9NDt geI+Nv145HjulO7bI3NT048AEQEAAc0kU2FoaWwgU2lkZGlxIDxpY2VnYW1iaXQ5MUBnbWFp bC5jb20+wsENBBMBCAA3FiEERtYfQYWFu+uAZjYrrzGlXdb6f1cFAmcgaYEFCQWjmoACGwME CwkIBwUVCAkKCwUWAgMBAAAKCRCvMaVd1vp/V/nnC/9KnNIr4a3JW3E/snxv1+XIyUmHBDLn PKBmLDYxO9RJe1xKo/sNmLEno4c8G1F/y12TLV086cpBYGKkE8mPMBABqxuiPG8srwoKc2HW bvoC2Zfeu/WeQ0YqeI9ZEwRhsDGQZ7vc8PnKnEUaPZn6iWW4GeX7dXWeGNrK0wU2B04l2d+M FIKaoPHk8w5Ff++QNcn0YRkm//nYlukHUrMxhNcuc18jaLLftOh7BH/4EbKtTN75KAFePQBi I2CbuC41fchTt12QrPB3yz1GKfudsEMLFHBNeComJNnuolPOq0YSyuKdRO8Jubn5ZqWQeTwj XbG7wTonDc8xe46irOhz36VcjsjSY+PYhVZSeDWeDUZgpaJkBjQDDodIN2eoMwVEyUByos9H mKrqrpBMmylOspAZzqjb5FtOqM0BCxQINdKKiMwRelSb6pHYCrbS0XzpwDUEpp7RWCbHgg+6 Ot72kQCEFxj2LzX9VxF24GGQy9inlUfN51IV04klSibtBuuz/NbOwM0EZyBpgQEMAJelVX4k CtCxD4Ji3FQ8LZs22z7VoUvqIb7Gj2lNvhPeijlqqBkSMIgnSCLxlH4ahqKnEV58IrfVriV0 92zb94Az2nl0r+bZYfvev1qCcVIYxk+pYYcRl5qPXX8XGalrkcBBWmkgTSwzNK9rV4850iVI hsJNel49qen9JwiFYMSKa2MYgdYSbeuuwXwUp0ZHeVFc5RnPK2wxws1xcnsdb9hRXs2UeTEE 0klG3HuXqJ96DzKrCieKHLjs330h+16gDWAFZSEoT7Mh3HFGI2dscVuBstQNgnwUMnsJv8jx c005CfLCjCBnJEhMd2/QFuLwCZv4IdoghKwYw18e61UbX2bFovo9dduD527pD4sFqi7U7ofv aO3yf+ulL6jiKypGvnbiBP3KY3aKxx6pHHH3aDc9eOqCUgrtS3+xt1du4+qxrYqEnrywFoJy 5zqSzbnTTjFpdTbY5SS52fIOktLlAKzEg6V9hkg2r08hC3/L4NVj6I4tsGZlqb2neRlHFmCr bQARAQABwsD8BBgBCAAmFiEERtYfQYWFu+uAZjYrrzGlXdb6f1cFAmcgaYIFCQWjmoACGwwA CgkQrzGlXdb6f1fDIgwAmpB7eL3XNSx3F+gbmksOPMqCU5rEswRedjEt6tBzFTXhdNFfhZTb vCddUNePZnzddgxAnDBcTqI1jx6Go6Hkti/mxJqXSczMYBsImD/lEm47axsADvpnNaEM+tmu m/cMKfpILUpy2Ey7CKXUA1vpzYeUD29EQWi0fxM0arplrVt/uzUdFRFQRn2hCqeDLBLONX1F Adq+re6M0dhKl4a2+erzZRIXh3vIGiDmpJEGrajrhqEnMXFp6toSiMGian94m8H3NT6rB64E JmdHgyjXADFbn2G5Mb6Pwa8KnnK1kYcZ+Pwu9LfMXfgI01Sh/k01hjUVmnpYep4nHUfwXA8r kn6WekD80DYbAfKyFAXQCO/nclZ82RNmJbDRi3AeMFrxKi6KgdGCp1Izhj9USaMOVqcuV2p0 Rsoq+sFqWOKaHWnQHCM9RkynQVqrgUaSawEbGlCP1KIhVmjfjVsmsCaKkUb9T6VeO+ZNe+Pn rPgMe6IIvn24UuW2f6fIt0AaqOWq In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=2607:f8b0:4864:20::430; envelope-from=icegambit91@gmail.com; helo=mail-pf1-x430.google.com X-Spam_score_int: -17 X-Spam_score: -1.8 X-Spam_bar: - X-Spam_report: (-1.8 / 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_ENVFROM_END_DIGIT=0.25, 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 Hi, Thank you for your reply. On 12/16/24 2:09 PM, Eugenio Perez Martin wrote: > On Sun, Dec 15, 2024 at 6:27 PM Sahil Siddiq wrote: >> On 12/10/24 2:57 PM, Eugenio Perez Martin wrote: >>> On Thu, Dec 5, 2024 at 9:34 PM Sahil Siddiq wrote: >>>> [...] >>>> I have been following the "Hands on vDPA: what do you do >>>> when you ain't got the hardware v2 (Part 2)" [1] blog to >>>> test my changes. To boot the L1 VM, I ran: >>>> >>>> sudo ./qemu/build/qemu-system-x86_64 \ >>>> -enable-kvm \ >>>> -drive file=//home/valdaarhun/valdaarhun/qcow2_img/L1.qcow2,media=disk,if=virtio \ >>>> -net nic,model=virtio \ >>>> -net user,hostfwd=tcp::2222-:22 \ >>>> -device intel-iommu,snoop-control=on \ >>>> -device virtio-net-pci,netdev=net0,disable-legacy=on,disable-modern=off,iommu_platform=on,guest_uso4=off,guest_uso6=off,host_uso=off,guest_announce=off,ctrl_vq=on,ctrl_rx=on,packed=on,event_idx=off,bus=pcie.0,addr=0x4 \ >>>> -netdev tap,id=net0,script=no,downscript=no \ >>>> -nographic \ >>>> -m 8G \ >>>> -smp 4 \ >>>> -M q35 \ >>>> -cpu host 2>&1 | tee vm.log >>>> >>>> Without "guest_uso4=off,guest_uso6=off,host_uso=off, >>>> guest_announce=off" in "-device virtio-net-pci", QEMU >>>> throws "vdpa svq does not work with features" [2] when >>>> trying to boot L2. >>>> >>>> The enums added in commit #2 in this series is new and >>>> wasn't in the earlier versions of the series. Without >>>> this change, x-svq=true throws "SVQ invalid device feature >>>> flags" [3] and x-svq is consequently disabled. >>>> >>>> The first issue is related to running traffic in L2 >>>> with vhost-vdpa. >>>> >>>> In L0: >>>> >>>> $ ip addr add 111.1.1.1/24 dev tap0 >>>> $ ip link set tap0 up >>>> $ ip addr show tap0 >>>> 4: tap0: mtu 1500 qdisc fq_codel state UNKNOWN group default qlen 1000 >>>> link/ether d2:6d:b9:61:e1:9a brd ff:ff:ff:ff:ff:ff >>>> inet 111.1.1.1/24 scope global tap0 >>>> valid_lft forever preferred_lft forever >>>> inet6 fe80::d06d:b9ff:fe61:e19a/64 scope link proto kernel_ll >>>> valid_lft forever preferred_lft forever >>>> >>>> I am able to run traffic in L2 when booting without >>>> x-svq. >>>> >>>> In L1: >>>> >>>> $ ./qemu/build/qemu-system-x86_64 \ >>>> -nographic \ >>>> -m 4G \ >>>> -enable-kvm \ >>>> -M q35 \ >>>> -drive file=//root/L2.qcow2,media=disk,if=virtio \ >>>> -netdev type=vhost-vdpa,vhostdev=/dev/vhost-vdpa-0,id=vhost-vdpa0 \ >>>> -device virtio-net-pci,netdev=vhost-vdpa0,disable-legacy=on,disable-modern=off,ctrl_vq=on,ctrl_rx=on,event_idx=off,bus=pcie.0,addr=0x7 \ >>>> -smp 4 \ >>>> -cpu host \ >>>> 2>&1 | tee vm.log >>>> >>>> In L2: >>>> >>>> # ip addr add 111.1.1.2/24 dev eth0 >>>> # ip addr show eth0 >>>> 2: eth0: mtu 1500 qdisc fq_codel state UP group default qlen 1000 >>>> link/ether 52:54:00:12:34:57 brd ff:ff:ff:ff:ff:ff >>>> altname enp0s7 >>>> inet 111.1.1.2/24 scope global eth0 >>>> valid_lft forever preferred_lft forever >>>> inet6 fe80::9877:de30:5f17:35f9/64 scope link noprefixroute >>>> valid_lft forever preferred_lft forever >>>> >>>> # ip route >>>> 111.1.1.0/24 dev eth0 proto kernel scope link src 111.1.1.2 >>>> >>>> # ping 111.1.1.1 -w3 >>>> PING 111.1.1.1 (111.1.1.1) 56(84) bytes of data. >>>> 64 bytes from 111.1.1.1: icmp_seq=1 ttl=64 time=0.407 ms >>>> 64 bytes from 111.1.1.1: icmp_seq=2 ttl=64 time=0.671 ms >>>> 64 bytes from 111.1.1.1: icmp_seq=3 ttl=64 time=0.291 ms >>>> >>>> --- 111.1.1.1 ping statistics --- >>>> 3 packets transmitted, 3 received, 0% packet loss, time 2034ms >>>> rtt min/avg/max/mdev = 0.291/0.456/0.671/0.159 ms >>>> >>>> >>>> But if I boot L2 with x-svq=true as shown below, I am unable >>>> to ping the host machine. >>>> >>>> $ ./qemu/build/qemu-system-x86_64 \ >>>> -nographic \ >>>> -m 4G \ >>>> -enable-kvm \ >>>> -M q35 \ >>>> -drive file=//root/L2.qcow2,media=disk,if=virtio \ >>>> -netdev type=vhost-vdpa,vhostdev=/dev/vhost-vdpa-0,x-svq=true,id=vhost-vdpa0 \ >>>> -device virtio-net-pci,netdev=vhost-vdpa0,disable-legacy=on,disable-modern=off,ctrl_vq=on,ctrl_rx=on,event_idx=off,bus=pcie.0,addr=0x7 \ >>>> -smp 4 \ >>>> -cpu host \ >>>> 2>&1 | tee vm.log >>>> >>>> In L2: >>>> >>>> # ip addr add 111.1.1.2/24 dev eth0 >>>> # ip addr show eth0 >>>> 2: eth0: mtu 1500 qdisc fq_codel state UP group default qlen 1000 >>>> link/ether 52:54:00:12:34:57 brd ff:ff:ff:ff:ff:ff >>>> altname enp0s7 >>>> inet 111.1.1.2/24 scope global eth0 >>>> valid_lft forever preferred_lft forever >>>> inet6 fe80::9877:de30:5f17:35f9/64 scope link noprefixroute >>>> valid_lft forever preferred_lft forever >>>> >>>> # ip route >>>> 111.1.1.0/24 dev eth0 proto kernel scope link src 111.1.1.2 >>>> >>>> # ping 111.1.1.1 -w10 >>>> PING 111.1.1.1 (111.1.1.1) 56(84) bytes of data. >>>> From 111.1.1.2 icmp_seq=1 Destination Host Unreachable >>>> ping: sendmsg: No route to host >>>> From 111.1.1.2 icmp_seq=2 Destination Host Unreachable >>>> From 111.1.1.2 icmp_seq=3 Destination Host Unreachable >>>> >>>> --- 111.1.1.1 ping statistics --- >>>> 3 packets transmitted, 0 received, +3 errors, 100% packet loss, time 2076ms >>>> pipe 3 >>>> >>>> The other issue is related to booting L2 with "x-svq=true" >>>> and "packed=on". >>>> >>>> In L1: >>>> >>>> $ ./qemu/build/qemu-system-x86_64 \ >>>> -nographic \ >>>> -m 4G \ >>>> -enable-kvm \ >>>> -M q35 \ >>>> -drive file=//root/L2.qcow2,media=disk,if=virtio \ >>>> -netdev type=vhost-vdpa,vhostdev=/dev/vhost-vdpa-0,id=vhost-vdpa0,x-svq=true \ >>>> -device virtio-net-pci,netdev=vhost-vdpa0,disable-legacy=on,disable-modern=off,guest_uso4=off,guest_uso6=off,host_uso=off,guest_announce=off,ctrl_vq=on,ctrl_rx=on,event_idx=off,packed=on,bus=pcie.0,addr=0x7 \ >>>> -smp 4 \ >>>> -cpu host \ >>>> 2>&1 | tee vm.log >>>> >>>> The kernel throws "virtio_net virtio1: output.0:id 0 is not >>>> a head!" [4]. >>>> >>> >>> So this series implements the descriptor forwarding from the guest to >>> the device in packed vq. We also need to forward the descriptors from >>> the device to the guest. The device writes them in the SVQ ring. >>> >>> The functions responsible for that in QEMU are >>> hw/virtio/vhost-shadow-virtqueue.c:vhost_svq_flush, which is called by >>> the device when used descriptors are written to the SVQ, which calls >>> hw/virtio/vhost-shadow-virtqueue.c:vhost_svq_get_buf. We need to do >>> modifications similar to vhost_svq_add: Make them conditional if we're >>> in split or packed vq, and "copy" the code from Linux's >>> drivers/virtio/virtio_ring.c:virtqueue_get_buf. >>> >>> After these modifications you should be able to ping and forward >>> traffic. As always, It is totally ok if it needs more than one >>> iteration, and feel free to ask any question you have :). >>> >> >> I misunderstood this part. While working on extending >> hw/virtio/vhost-shadow-virtqueue.c:vhost_svq_get_buf() [1] >> for packed vqs, I realized that this function and >> vhost_svq_flush() already support split vqs. However, I am >> unable to ping L0 when booting L2 with "x-svq=true" and >> "packed=off" or when the "packed" option is not specified >> in QEMU's command line. >> >> I tried debugging these functions for split vqs after running >> the following QEMU commands while following the blog [2]. >> >> Booting L1: >> >> $ sudo ./qemu/build/qemu-system-x86_64 \ >> -enable-kvm \ >> -drive file=//home/valdaarhun/valdaarhun/qcow2_img/L1.qcow2,media=disk,if=virtio \ >> -net nic,model=virtio \ >> -net user,hostfwd=tcp::2222-:22 \ >> -device intel-iommu,snoop-control=on \ >> -device virtio-net-pci,netdev=net0,disable-legacy=on,disable-modern=off,iommu_platform=on,guest_uso4=off,guest_uso6=off,host_uso=off,guest_announce=off,ctrl_vq=on,ctrl_rx=on,packed=off,event_idx=off,bus=pcie.0,addr=0x4 \ >> -netdev tap,id=net0,script=no,downscript=no \ >> -nographic \ >> -m 8G \ >> -smp 4 \ >> -M q35 \ >> -cpu host 2>&1 | tee vm.log >> >> Booting L2: >> >> # ./qemu/build/qemu-system-x86_64 \ >> -nographic \ >> -m 4G \ >> -enable-kvm \ >> -M q35 \ >> -drive file=//root/L2.qcow2,media=disk,if=virtio \ >> -netdev type=vhost-vdpa,vhostdev=/dev/vhost-vdpa-0,x-svq=true,id=vhost-vdpa0 \ >> -device virtio-net-pci,netdev=vhost-vdpa0,disable-legacy=on,disable-modern=off,ctrl_vq=on,ctrl_rx=on,event_idx=off,bus=pcie.0,addr=0x7 \ >> -smp 4 \ >> -cpu host \ >> 2>&1 | tee vm.log >> >> I printed out the contents of VirtQueueElement returned >> by vhost_svq_get_buf() in vhost_svq_flush() [3]. >> I noticed that "len" which is set by "vhost_svq_get_buf" >> is always set to 0 while VirtQueueElement.len is non-zero. >> I haven't understood the difference between these two "len"s. >> > > VirtQueueElement.len is the length of the buffer, while the len of > vhost_svq_get_buf is the bytes written by the device. In the case of > the tx queue, VirtQueuelen is the length of the tx packet, and the > vhost_svq_get_buf is always 0 as the device does not write. In the > case of rx, VirtQueueElem.len is the available length for a rx frame, > and the vhost_svq_get_buf len is the actual length written by the > device. > > To be 100% accurate a rx packet can span over multiple buffers, but > SVQ does not need special code to handle this. > > So vhost_svq_get_buf should return > 0 for rx queue (svq->vq->index == > 0), and 0 for tx queue (svq->vq->index % 2 == 1). > > Take into account that vhost_svq_get_buf only handles split vq at the > moment! It should be renamed or splitted into vhost_svq_get_buf_split. In L1, there are 2 virtio network devices. # lspci -nn | grep -i net 00:02.0 Ethernet controller [0200]: Red Hat, Inc. Virtio network device [1af4:1000] 00:04.0 Ethernet controller [0200]: Red Hat, Inc. Virtio 1.0 network device [1af4:1041] (rev 01) I am using the second one (1af4:1041) for testing my changes and have bound this device to the vp_vdpa driver. # vdpa dev show -jp { "dev": { "vdpa0": { "type": "network", "mgmtdev": "pci/0000:00:04.0", "vendor_id": 6900, "max_vqs": 3, "max_vq_size": 256 } } } The max number of vqs is 3 with the max size being 256. Since, there are 2 virtio net devices, vhost_vdpa_svqs_start [1] is called twice. For each of them. it calls vhost_svq_start [2] v->shadow_vqs->len number of times. Printing the values of dev->vdev->name, v->shadow_vqs->len and svq->vring.num in vhost_vdpa_svqs_start gives: name: virtio-net len: 2 num: 256 num: 256 name: virtio-net len: 1 num: 64 I am not sure how to match the above log lines to the right virtio-net device since the actual value of num can be less than "max_vq_size" in the output of "vdpa dev show". I think the first 3 log lines correspond to the virtio net device that I am using for testing since it has 2 vqs (rx and tx) while the other virtio-net device only has one vq. When printing out the values of svq->vring.num, used_elem.len and used_elem.id in vhost_svq_get_buf, there are two sets of output. One set corresponds to svq->vring.num = 64 and the other corresponds to svq->vring.num = 256. For svq->vring.num = 64, only the following line is printed repeatedly: size: 64, len: 1, i: 0 For svq->vring.num = 256, the following line is printed 20 times, size: 256, len: 0, i: 0 followed by: size: 256, len: 0, i: 1 size: 256, len: 0, i: 1 used_elem.len is used to set the value of len that is returned by vhost_svq_get_buf, and it's always 0. So the value of "len" returned by vhost_svq_get_buf when called in vhost_svq_flush is also 0. Thanks, Sahil [1] https://gitlab.com/qemu-project/qemu/-/blob/master/hw/virtio/vhost-vdpa.c#L1243 [2] https://gitlab.com/qemu-project/qemu/-/blob/master/hw/virtio/vhost-vdpa.c#L1265