On Wed, Jul 19, 2023 at 08:35:50PM +0800, Hawkins Jiawei wrote: > 在 2023/7/19 17:11, Michael S. Tsirkin 写道: > > On Wed, Jul 19, 2023 at 03:53:45PM +0800, Hawkins Jiawei wrote: > >> This patchset allows QEMU to delay polling and checking the device > >> used buffer until either the SVQ is full or control commands shadow > >> buffers are full, instead of polling and checking immediately after > >> sending each SVQ control command, so that QEMU can send all the SVQ > >> control commands in parallel, which have better performance improvement. > >> > >> I use vp_vdpa device to simulate vdpa device, and create 4094 VLANS in > >> guest to build a test environment for sending multiple CVQ state load > >> commands. This patch series can improve latency from 10023 us to > >> 8697 us for about 4099 CVQ state load commands, about 0.32 us per command. > > > > Looks like a tiny improvement. > > At the same time we have O(n^2) behaviour with memory mappings. > > Hi Michael, > > Thanks for your review. > > I wonder why you say "we have O(n^2) behaviour on memory mappings" here?
it's not specific to virtio - it's related to device init. generally each device has some memory. during boot bios enables each individually O(n) where n is # of devices. memory maps has to be updated and in qemu this update is at least superlinear with n (more like O(n log n) I think). This gets up > O(n^2) with n number of devices. > From my understanding, QEMU maps two page-size buffers as control > commands shadow buffers at device startup. These buffers then are used > to cache SVQ control commands, where QEMU fills them with multiple SVQ control > commands bytes, flushes them when SVQ descriptors are full or these > control commands shadow buffers reach their capacity. > > QEMU repeats this process until all CVQ state load commands have been > sent in loading. > > In this loading process, only control commands shadow buffers > translation should be relative to memory mappings, which should be > O(log n) behaviour to my understanding(Please correct me if I am wrong). > > > Not saying we must not do this but I think it's worth > > checking where the bottleneck is. My guess would be > > vp_vdpa is not doing things in parallel. Want to try fixing that > > As for "vp_vdpa is not doing things in parallel.", do you mean > the vp_vdpa device cannot process QEMU's SVQ control commands > in parallel? > > In this situation, I will try to use real vdpa hardware to > test the patch series performance. yea, pls do that. > > to see how far it can be pushed? > > Currently, I am involved in the "Add virtio-net Control Virtqueue state > restore support" project in Google Summer of Code now. Because I am > uncertain about the time it will take to fix that problem in the vp_vdpa > device, I prefer to complete the gsoc project first. > > Thanks! > > > > > > > >> Note that this patch should be based on > >> patch "Vhost-vdpa Shadow Virtqueue VLAN support" at [1]. > >> > >> [1]. https://lists.gnu.org/archive/html/qemu-devel/2023-07/msg03719.html > >> > >> TestStep > >> ======== > >> 1. regression testing using vp-vdpa device > >> - For L0 guest, boot QEMU with two virtio-net-pci net device with > >> `ctrl_vq`, `ctrl_rx`, `ctrl_rx_extra` features on, command line like: > >> -device virtio-net-pci,disable-legacy=on,disable-modern=off, > >> iommu_platform=on,mq=on,ctrl_vq=on,guest_announce=off, > >> indirect_desc=off,queue_reset=off,ctrl_rx=on,ctrl_rx_extra=on,... > >> > >> - For L1 guest, apply the patch series and compile the source code, > >> start QEMU with two vdpa device with svq mode on, enable the `ctrl_vq`, > >> `ctrl_rx`, `ctrl_rx_extra` features on, command line like: > >> -netdev type=vhost-vdpa,x-svq=true,... > >> -device virtio-net-pci,mq=on,guest_announce=off,ctrl_vq=on, > >> ctrl_rx=on,ctrl_rx_extra=on... > >> > >> - For L2 source guest, run the following bash command: > >> ```bash > >> #!/bin/sh > >> > >> for idx1 in {0..9} > >> do > >> for idx2 in {0..9} > >> do > >> for idx3 in {0..6} > >> do > >> ip link add macvlan$idx1$idx2$idx3 link eth0 > >> address 4a:30:10:19:$idx1$idx2:1$idx3 type macvlan mode bridge > >> ip link set macvlan$idx1$idx2$idx3 up > >> done > >> done > >> done > >> ``` > >> - Execute the live migration in L2 source monitor > >> > >> - Result > >> * with this series, QEMU should not trigger any error or warning. > >> > >> > >> > >> 2. perf using vp-vdpa device > >> - For L0 guest, boot QEMU with two virtio-net-pci net device with > >> `ctrl_vq`, `ctrl_vlan` features on, command line like: > >> -device virtio-net-pci,disable-legacy=on,disable-modern=off, > >> iommu_platform=on,mq=on,ctrl_vq=on,guest_announce=off, > >> indirect_desc=off,queue_reset=off,ctrl_vlan=on,... > >> > >> - For L1 guest, apply the patch series, then apply an addtional > >> patch to record the load time in microseconds as following: > >> ```diff > >> diff --git a/hw/net/vhost_net.c b/hw/net/vhost_net.c > >> index 6b958d6363..501b510fd2 100644 > >> --- a/hw/net/vhost_net.c > >> +++ b/hw/net/vhost_net.c > >> @@ -295,7 +295,10 @@ static int vhost_net_start_one(struct vhost_net *net, > >> } > >> > >> if (net->nc->info->load) { > >> + int64_t start_us = g_get_monotonic_time(); > >> r = net->nc->info->load(net->nc); > >> + error_report("vhost_vdpa_net_load() = %ld us", > >> + g_get_monotonic_time() - start_us); > >> if (r < 0) { > >> goto fail; > >> } > >> ``` > >> > >> - For L1 guest, compile the code, and start QEMU with two vdpa device > >> with svq mode on, enable the `ctrl_vq`, `ctrl_vlan` features on, > >> command line like: > >> -netdev type=vhost-vdpa,x-svq=true,... > >> -device virtio-net-pci,mq=on,guest_announce=off,ctrl_vq=on, > >> ctrl_vlan=on... > >> > >> - For L2 source guest, run the following bash command: > >> ```bash > >> #!/bin/sh > >> > >> for idx in {1..4094} > >> do > >> ip link add link eth0 name vlan$idx type vlan id $idx > >> done > >> ``` > >> > >> - wait for some time, then execute the live migration in L2 source > >> monitor > >> > >> - Result > >> * with this series, QEMU should not trigger any warning > >> or error except something like "vhost_vdpa_net_load() = 8697 us" > >> * without this series, QEMU should not trigger any warning > >> or error except something like "vhost_vdpa_net_load() = 10023 us" > >> > >> ChangeLog > >> ========= > >> v3: > >> - refactor vhost_svq_poll() to accept cmds_in_flight > >> suggested by Jason and Eugenio > >> - refactor vhost_vdpa_net_cvq_add() to make control commands buffers > >> is not tied to `s->cvq_cmd_out_buffer` and `s->status`, so we can reuse > >> it suggested by Eugenio > >> - poll and check when SVQ is full or control commands shadow buffers is > >> full > >> > >> v2: https://lore.kernel.org/all/cover.1683371965.git.yin31...@gmail.com/ > >> - recover accidentally deleted rows > >> - remove extra newline > >> - refactor `need_poll_len` to `cmds_in_flight` > >> - return -EINVAL when vhost_svq_poll() return 0 or check > >> on buffers written by device fails > >> - change the type of `in_cursor`, and refactor the > >> code for updating cursor > >> - return directly when vhost_vdpa_net_load_{mac,mq}() > >> returns a failure in vhost_vdpa_net_load() > >> > >> v1: https://lore.kernel.org/all/cover.1681732982.git.yin31...@gmail.com/ > >> > >> Hawkins Jiawei (8): > >> vhost: Add argument to vhost_svq_poll() > >> vdpa: Use iovec for vhost_vdpa_net_cvq_add() > >> vhost: Expose vhost_svq_available_slots() > >> vdpa: Avoid using vhost_vdpa_net_load_*() outside > >> vhost_vdpa_net_load() > >> vdpa: Check device ack in vhost_vdpa_net_load_rx_mode() > >> vdpa: Move vhost_svq_poll() to the caller of vhost_vdpa_net_cvq_add() > >> vdpa: Add cursors to vhost_vdpa_net_loadx() > >> vdpa: Send cvq state load commands in parallel > >> > >> hw/virtio/vhost-shadow-virtqueue.c | 38 ++-- > >> hw/virtio/vhost-shadow-virtqueue.h | 3 +- > >> net/vhost-vdpa.c | 354 ++++++++++++++++++----------- > >> 3 files changed, 249 insertions(+), 146 deletions(-) > >> > >> -- > >> 2.25.1 > >
