在 2023/7/19 20:46, Michael S. Tsirkin 写道: > 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.
Thanks for your explanation. > >> 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 >>> >
