[vfio-users] Poor networking performance in linux with sr-iov NICs

[Ryan Flagler]

I'm currently using a VF nic passed through to windows 10 with great
success. When I attempt to do the same with with a Linux guest machine, I
see a kernel warning in my dmesg output and the nic not only performs
poorly but also seems to cycle up and down from time to time. Any ideas?

The dmesg output.

[  102.828264] WARNING: CPU: 0 PID: 0 at
/build/linux-5EyXrQ/linux-4.4.0/net/sched/sch_generic.c:306
dev_watchdog+0x237/0x240()
[  102.828289] NETDEV WATCHDOG: ens3 (igbvf): transmit queue 0 timed out
[  102.828297] Modules linked in: ppdev kvm_intel kvm irqbypass joydev
input_leds serio_raw i2c_piix4 parport_pc parport 8250_fintek mac_hid
ib_iser rdma_cm iw_cm ib_cm ib_sa ib_mad ib_core ib_addr iscsi_tcp
libiscsi_tcp libiscsi scsi_transport_iscsi autofs4 btrfs raid10 raid456
async_raid6_recov async_memcpy async_pq async_xor async_tx xor raid6_pq
libcrc32c raid1 raid0 multipath linear hid_generic usbhid hid
crct10dif_pclmul crc32_pclmul ghash_clmulni_intel aesni_intel aes_x86_64
lrw gf128mul glue_helper ablk_helper cryptd psmouse igbvf pata_acpi floppy
[  102.828342] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.4.0-87-generic
#110-Ubuntu
[  102.828349] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
0.0.0 02/06/2015
[  102.828351]  0000000000000286 7717ad27f8874148 ffff88013fc03d98
ffffffff813f9903
[  102.828354]  ffff88013fc03de0 ffffffff81d70f18 ffff88013fc03dd0
ffffffff81081332
[  102.828356]  0000000000000000 ffff8801384b0480 0000000000000000
ffff88003527a000
[  102.828358] Call Trace:
[  102.828359]  <IRQ>  [<ffffffff813f9903>] dump_stack+0x63/0x90
[  102.828367]  [<ffffffff81081332>] warn_slowpath_common+0x82/0xc0
[  102.828369]  [<ffffffff810813cc>] warn_slowpath_fmt+0x5c/0x80
[  102.828372]  [<ffffffff8175db97>] dev_watchdog+0x237/0x240
[  102.828375]  [<ffffffff8175d960>] ? qdisc_rcu_free+0x40/0x40
[  102.828379]  [<ffffffff810ecf25>] call_timer_fn+0x35/0x120
[  102.828381]  [<ffffffff8175d960>] ? qdisc_rcu_free+0x40/0x40
[  102.828388]  [<ffffffff810ed8da>] run_timer_softirq+0x23a/0x2f0
[  102.828390]  [<ffffffff81085e11>] __do_softirq+0x101/0x290
[  102.828393]  [<ffffffff81086113>] irq_exit+0xa3/0xb0
[  102.828396]  [<ffffffff81844962>] smp_apic_timer_interrupt+0x42/0x50
[  102.828400]  [<ffffffff81842c22>] apic_timer_interrupt+0x82/0x90
[  102.828401]  <EOI>  [<ffffffff81064636>] ? native_safe_halt+0x6/0x10
[  102.828407]  [<ffffffff81038e5e>] default_idle+0x1e/0xe0
[  102.828409]  [<ffffffff8103966f>] arch_cpu_idle+0xf/0x20
[  102.828413]  [<ffffffff810c468a>] default_idle_call+0x2a/0x40
[  102.828415]  [<ffffffff810c49f1>] cpu_startup_entry+0x2f1/0x350
[  102.828418]  [<ffffffff8183570c>] rest_init+0x7c/0x80
[  102.828422]  [<ffffffff81f5e011>] start_kernel+0x481/0x4a2
[  102.828425]  [<ffffffff81f5d120>] ? early_idt_handler_array+0x120/0x120
[  102.828427]  [<ffffffff81f5d339>] x86_64_start_reservations+0x2a/0x2c
[  102.828429]  [<ffffffff81f5d485>] x86_64_start_kernel+0x14a/0x16d
[  102.828434] ---[ end trace 3dd091553181e0bf ]---

Thanks!
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