From: bugzilla@dpdk.org
To: dev@dpdk.org
Subject: [DPDK/other Bug 1867] mlx5: enabling internal VF-to-VF communication causes performance to drop significantly
Date: Tue, 13 Jan 2026 12:31:28 +0000 [thread overview]
Message-ID: <bug-1867-3@http.bugs.dpdk.org/> (raw)
http://bugs.dpdk.org/show_bug.cgi?id=1867
Bug ID: 1867
Summary: mlx5: enabling internal VF-to-VF communication causes
performance to drop significantly
Product: DPDK
Version: 25.11
Hardware: All
OS: All
Status: UNCONFIRMED
Severity: normal
Priority: Normal
Component: other
Assignee: dev@dpdk.org
Reporter: robin@jarry.cc
CC: rasland@nvidia.com
Target Milestone: ---
SUMMARY
=======
Enabling internal VF-to-VF communication causes performance to drop
significantly.
Here is a visual representation of the topology:
+---------------------------------------------------------------------+
| dut |
| |
| +---------------+ +-------------+ +---------------+ |
| | testpmd | | testpmd | | testpmd | |
| | "outer 0" | | "inner" | | "outer 1" | |
| +--+---------+--+ +--+-------+--+ +--+---------+--+ |
| | | | | | | |
| | | ,-------' `-------. | | |
| | | | | | | |
| +--+--+ +--+--+ +--+--+ +--+--+ +--+--+ +--+--+ |
| | vf0 | | vf1 | | vf2 | | vf2 | | vf1 | | vf0 | |
| +--+--+ +--+--+ +--+--+ +--+--+ +--+--+ +--+--+ |
| | | | | | | |
| | | | | | | |
| +--+---------|-------|--+ +--|-------|---------+--+ |
| | `-------' | | `-------' | |
| | pf0 | | pf1 | |
| +-----------+-----------+ +-----------+-----------+ |
| | | |
+-------------|-----------------------------------------|-------------+
| |
+-------------|-----------------------------------------|-------------+
| | switch | |
+-------------|-----------------------------------------|-------------+
| |
+-------------|-----------------------------------------|-------------+
| | | |
| +-----------+------------+ +-----------+-----------+ |
| | pf0 | | pf1 | |
| +-----------+------------+ +-----------+-----------+ |
| | | |
| +-----------+-----------------------------------------+-----------+ |
| | | |
| | trex | |
| | | |
| +-----------------------------------------------------------------+ |
| |
| tgen |
+---------------------------------------------------------------------+
Important notes:
* Promisc mode is *disabled* on all ports.
* Traffic is sent from trex with VF0 mac addresses as ethernet destination.
* The switch does *not* flood anything.
Observations:
* When the tgen emits at 1M pkt/s per side, every packet is properly forwarded
to both "outer" testpmds.
* When emitting at 10M pkt/s per side, only ~6.8M pkt/s are received by the
"outer" testpmds on VF0.
* When emitting at 37.5M pkt/s (25G line rate), only ~1.5M pkt/s are received
by the "outer" testpmds on VF0.
* ethtool stats on PF interfaces reflect the actual transmission rate of the
traffic generator (rx_packets_phy) but only a portion of these are relayed to
VF0.
With this simpler setup:
+--------------------------+
| dut |
| |
| +--------------+ |
| | testpmd | |
| +--+-------+---+ |
| | | |
| | | |
| | | |
| +--+--+ +--+--+ |
| | vf0 | | vf1 | |
| +--+--+ +--+--+ |
| | | |
| | | |
| +--|-------|-----+ |
| | \ / | |
| | \ / pf0 | |
| +----\ /--------+ |
| || |
+-------||-----------------+
||
+-------||---------------------------------+
| || |
| |\--------------------------\ |
| | switch | |
| | | |
+-------|---------------------------|------+
| |
+-------|---------------------------|------+
| | | |
| +-----+-----+ +----+----+ |
| | pf0 | | pf1 | |
| +-----+-----+ +----+----+ |
| | | |
| +-----+---------------------------+----+ |
| | | |
| | trex | |
| | | |
| +--------------------------------------+ |
| |
| tgen |
+------------------------------------------+
The maximum line rate of the port can be achieved (37.5M pkt/s total, 18.75M
pkt/s per side).
SOFTWARE
========
~/dpdk# git describe
v25.11-4-gcd60dcd503b9
~# cat /proc/cmdline
BOOT_IMAGE=(hd0,gpt2)/vmlinuz-6.16.7-100.fc41.x86_64 ... \
intel_iommu=on iommu=pt default_hugepagesz=1GB hugepagesz=1G
hugepages=32 \
skew_tick=1 tsc=reliable rcupdate.rcu_normal_after_boot=1 nohz=on \
isolcpus=10-19,30-39 nohz_full=10-19,30-39 rcu_nocbs=10-19,30-39 \
tuned.non_isolcpus=3ff003ff intel_pstate=passive nosoftlockup
libibverbs.so.1.14.51.0
libmlx5.so.1.24.51.0
HARDWARE
========
CPU Model name: Intel(R) Xeon(R) Silver 4316 CPU @
2.30GHz
SLOT DRIVER IFNAME MAC LINK/STATE SPEED
DEVICE
0000:18:00.0 mlx5_core enp24s0f0np0 b8:3f:d2:fa:53:86 1/up 25Gb/s
MT2894 Family [ConnectX-6 Lx]
0000:18:00.1 mlx5_core enp24s0f1np1 b8:3f:d2:fa:53:87 1/up 25Gb/s
MT2894 Family [ConnectX-6 Lx]
0000:18:00.2 mlx5_core enp24s0f0v0 02:aa:aa:aa:aa:00 1/up 25Gb/s
ConnectX Family mlx5Gen Virtual Function
0000:18:00.3 mlx5_core enp24s0f0v1 02:aa:aa:aa:aa:01 1/up 25Gb/s
ConnectX Family mlx5Gen Virtual Function
0000:18:00.4 mlx5_core enp24s0f0v2 02:aa:aa:aa:aa:02 1/up 25Gb/s
ConnectX Family mlx5Gen Virtual Function
0000:18:08.2 mlx5_core enp24s0f1v0 02:cc:cc:cc:cc:00 1/up 25Gb/s
ConnectX Family mlx5Gen Virtual Function
0000:18:08.3 mlx5_core enp24s0f1v1 02:cc:cc:cc:cc:01 1/up 25Gb/s
ConnectX Family mlx5Gen Virtual Function
0000:18:08.4 mlx5_core enp24s0f1v2 02:cc:cc:cc:cc:02 1/up 25Gb/s
ConnectX Family mlx5Gen Virtual Function
~# ethtool -i enp24s0f0np0
driver: mlx5_core
version: 6.16.7-100.fc41.x86_64
firmware-version: 26.41.1000 (MT_0000000532)
expansion-rom-version:
bus-info: 0000:18:00.0
supports-statistics: yes
supports-test: yes
supports-eeprom-access: no
supports-register-dump: no
supports-priv-flags: yes
~# ethtool -i enp24s0f1np1
driver: mlx5_core
version: 6.16.7-100.fc41.x86_64
firmware-version: 26.41.1000 (MT_0000000532)
expansion-rom-version:
bus-info: 0000:18:00.1
supports-statistics: yes
supports-test: yes
supports-eeprom-access: no
supports-register-dump: no
supports-priv-flags: yes
VF CONFIGURATION
================
+ pf0=enp24s0f0np0
+ pf1=enp24s0f1np1
+++ readlink -ve /sys/class/net/enp24s0f0np0/device
++ basename /sys/devices/pci0000:17/0000:17:02.0/0000:18:00.0
+ pci=0000:18:00.0
+ devlink dev eswitch set pci/0000:18:00.0 mode legacy
+ echo 1
+ tee /sys/class/net/enp24s0f0np0/device/sriov_drivers_autoprobe
1
+ echo 3
+ tee /sys/class/net/enp24s0f0np0/device/sriov_numvfs
3
+ ip link set enp24s0f0np0 vf 0 mac 02:aa:aa:aa:aa:00
+ ip link set enp24s0f0np0 vf 1 mac 02:aa:aa:aa:aa:01
+ ip link set enp24s0f0np0 vf 2 mac 02:aa:aa:aa:aa:02
+ ip link set enp24s0f0v0 address 02:aa:aa:aa:aa:00
+ ip link set enp24s0f0v0 up
+ ip link set enp24s0f0v1 address 02:aa:aa:aa:aa:01
+ ip link set enp24s0f0v1 up
+ ip link set enp24s0f0v2 address 02:aa:aa:aa:aa:02
+ ip link set enp24s0f0v2 up
+++ readlink -ve /sys/class/net/enp24s0f0np0/device/virtfn0
++ basename /sys/devices/pci0000:17/0000:17:02.0/0000:18:00.2
+ vf00_pci=0000:18:00.2
+++ readlink -ve /sys/class/net/enp24s0f0np0/device/virtfn1
++ basename /sys/devices/pci0000:17/0000:17:02.0/0000:18:00.3
+ vf01_pci=0000:18:00.3
+++ readlink -ve /sys/class/net/enp24s0f0np0/device/virtfn2
++ basename /sys/devices/pci0000:17/0000:17:02.0/0000:18:00.4
+ vf02_pci=0000:18:00.4
+++ readlink -ve /sys/class/net/enp24s0f1np1/device
++ basename /sys/devices/pci0000:17/0000:17:02.0/0000:18:00.1
+ pci=0000:18:00.1
+ devlink dev eswitch set pci/0000:18:00.1 mode legacy
+ echo 1
+ tee /sys/class/net/enp24s0f1np1/device/sriov_drivers_autoprobe
1
+ echo 3
+ tee /sys/class/net/enp24s0f1np1/device/sriov_numvfs
3
+++ readlink -ve /sys/class/net/enp24s0f1np1/device/virtfn0
++ basename /sys/devices/pci0000:17/0000:17:02.0/0000:18:08.2
+ vf10_pci=0000:18:08.2
+++ readlink -ve /sys/class/net/enp24s0f1np1/device/virtfn1
++ basename /sys/devices/pci0000:17/0000:17:02.0/0000:18:08.3
+ vf11_pci=0000:18:08.3
+++ readlink -ve /sys/class/net/enp24s0f1np1/device/virtfn2
++ basename /sys/devices/pci0000:17/0000:17:02.0/0000:18:08.4
+ vf12_pci=0000:18:08.4
+ ip link set enp24s0f1np1 vf 0 mac 02:cc:cc:cc:cc:00
+ ip link set enp24s0f1np1 vf 1 mac 02:cc:cc:cc:cc:01
+ ip link set enp24s0f1np1 vf 2 mac 02:cc:cc:cc:cc:02
+ ip link set enp24s0f1v0 address 02:cc:cc:cc:cc:00
+ ip link set enp24s0f1v0 up
+ ip link set enp24s0f1v1 address 02:cc:cc:cc:cc:01
+ ip link set enp24s0f1v1 up
+ ip link set enp24s0f1v2 address 02:cc:cc:cc:cc:02
+ ip link set enp24s0f1v2 up
TESTPMD COMMANDS
================
~# cat ./testpmd
set promisc all off
RUNTIME_DIRECTORY=/tmp/outer0 dpdk-testpmd -n 4 -l 0,12,32,13,33 -a
0000:18:00.2 -a 0000:18:00.3 -- \
--nb-cores 4 --rxq=4 --txq=4 --rxd=2048 --txd=2048 --forward-mode=mac
-i \
--eth-peer=0,30:3e:a7:0b:f2:54 --eth-peer=1,02:aa:aa:aa:aa:02 \
--rss-udp --auto-start --cmdline-file=./testpmd --record-burst-stats
RUNTIME_DIRECTORY=/tmp/inner dpdk-testpmd -n 4 -l 0,14,34,15,35 -a 0000:18:00.4
-a 0000:18:08.4 -- \
--nb-cores 4 --rxq=4 --txq=4 --rxd=2048 --txd=2048 --forward-mode=mac
-i \
--eth-peer=0,02:aa:aa:aa:aa:01 --eth-peer=1,02:cc:cc:cc:cc:01 \
--rss-udp --auto-start --cmdline-file=./testpmd --record-burst-stats
RUNTIME_DIRECTORY=/tmp/outer1 dpdk-testpmd -n 4 -l 0,10,30,11,31 -a
0000:18:08.2 -a 0000:18:08.3 -- \
--nb-cores 4 --rxq=4 --txq=4 --rxd=2048 --txd=2048 --forward-mode=mac
-i \
--eth-peer=0,30:3e:a7:0b:f2:55 --eth-peer=1,02:cc:cc:cc:cc:02 \
--rss-udp --auto-start --cmdline-file=./testpmd --record-burst-stats
--
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