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Thu, 19 Dec 2024 11:37:38 -0800 (PST) Received: from [192.168.1.18] ([223.233.80.80]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-72aad8fd2fdsm1681931b3a.156.2024.12.19.11.37.35 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 19 Dec 2024 11:37:37 -0800 (PST) Message-ID: <9b20ffc4-b55b-42c8-9847-a677c30c0051@gmail.com> Date: Fri, 20 Dec 2024 01:07:28 +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::52d; envelope-from=icegambit91@gmail.com; helo=mail-pg1-x52d.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, On 12/17/24 1:20 PM, Eugenio Perez Martin wrote: > On Tue, Dec 17, 2024 at 6:45 AM Sahil Siddiq wrote: >> 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, > > How is max_vqs=3? For this to happen L0 QEMU should have > virtio-net-pci,...,queues=3 cmdline argument. I am not sure why max_vqs is 3. I haven't set the value of queues to 3 in the cmdline argument. Is max_vqs expected to have a default value other than 3? In the blog [1] as well, max_vqs is 3 even though there's no queues=3 argument. > It's clear the guest is not using them, we can add mq=off > to simplify the scenario. The value of max_vqs is still 3 after adding mq=off. The whole command that I run to boot L0 is: $ 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,mq=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 Could it be that 2 of the 3 vqs are used for the dataplane and the third vq is the control vq? >> "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. >> > > Ok I understand this confusion, as the code is not intuitive :). Take > into account you can only have svq in vdpa devices, so both > vhost_vdpa_svqs_start are acting on the vdpa device. > > You are seeing two calls to vhost_vdpa_svqs_start because virtio (and > vdpa) devices are modelled internally as two devices in QEMU: One for > the dataplane vq, and other for the control vq. There are historical > reasons for this, but we use it in vdpa to always shadow the CVQ while > leaving dataplane passthrough if x-svq=off and the virtio & virtio-net > feature set is understood by SVQ. > > If you break at vhost_vdpa_svqs_start with gdb and go higher in the > stack you should reach vhost_net_start, that starts each vhost_net > device individually. > > To be 100% honest, each dataplain *queue pair* (rx+tx) is modelled > with a different vhost_net device in QEMU, but you don't need to take > that into account implementing the packed vq :). Got it, this makes sense now. >> 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 > > First QEMU's vhost_net device, the dataplane. > >> name: virtio-net >> len: 1 >> num: 64 >> > > Second QEMU's vhost_net device, the control virtqueue. Ok, if I understand this correctly, the control vq doesn't need separate queues for rx and tx. >> 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". >> > > Yes, the device can set a different vq max per vq, and the driver can > negotiate a lower vq size per vq too. > >> 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 >> > > This is with packed=off, right? If this is testing with packed, you > need to change the code to accommodate it. Let me know if you need > more help with this. Yes, this is for packed=off. For the time being, I am trying to get L2 to communicate with L0 using split virtqueues and x-svq=true. > In the CVQ the only reply is a byte, indicating if the command was > applied or not. This seems ok to me. Understood. > The queue can also recycle ids as long as they are not available, so > that part seems correct to me too. I am a little confused here. The ids are recycled when they are available (i.e., the id is not already in use), right? >> 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 >> > > This makes sense for the tx queue too. Can you print the VirtQueue index? For svq->vring.num = 64, the vq index is 2. So the following line (svq->vring.num, used_elem.len, used_elem.id, svq->vq->queue_index) is printed repeatedly: size: 64, len: 1, i: 0, vq idx: 2 For svq->vring.num = 256, the following line is repeated several times: size: 256, len: 0, i: 0, vq idx: 1 This is followed by: size: 256, len: 0, i: 1, vq idx: 1 In both cases, queue_index is 1. To get the value of queue_index, I used "virtio_get_queue_index(svq->vq)" [2]. Since the queue_index is 1, I guess this means this is the tx queue and the value of len (0) is correct. However, nothing with queue_index % 2 == 0 is printed by vhost_svq_get_buf() which means the device is not sending anything to the guest. Is this correct? >> 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 >> > Thanks, Sahil [1] https://www.redhat.com/en/blog/hands-vdpa-what-do-you-do-when-you-aint-got-hardware-part-2 [2] https://gitlab.com/qemu-project/qemu/-/blob/99d6a32469debf1a48921125879b614d15acfb7a/hw/virtio/virtio.c#L3454