Network benchmark—iperf3 single-thread lies

So I was running iperf3 on my GreenCloudVPS box and getting 3Gbps on a 10G port wey? Single thread, one stream. Thought I got scammed. Then I ran 10 parallel streams and hit 9.4Gbps. What gives?

Cpu was pinned to one core at 100%. Irqbalance running but useless. Found out virtio-net queues all landing on same cpu. This is a known thing but no one talks about it?

Anyway I wrote a little tune guide, maybe helps someone:

# check which cpu handles your nic
cat /proc/interrupts | grep virtio

# set affinity manually (example: spread across 0-3)
echo 1 > /proc/irq/XX/smp_affinity
echo 2 > /proc/irq/YY/smp_affinity
# etc

Cheers for detailed report! Sent ticket yesterday about same issue on my test order, they said "network is shared so speeds vary" — not helpful. Made test order on HostHatch (https://hosthatch.com) and same behavior, so probably virtio driver default across industry.

Your irq affinity fix works. I applied to production box, saw improvement immediately. Will add to internal docs.

One note: xps requires newer kernel than what GreenCloudVPS ships. You can build module yourself but check ToS first. Cheers!

Reproduced on Leaseweb, Time4VPS, Hostinger. All same pattern.

$ iperf3 -c target -t 10
[ ID] Interval           Transfer     Bitrate
[  5]   0.00-10.00  sec  3.42 GBytes  2.94 Gbits/sec

$ iperf3 -c target -t 10 -P 10
[SUM]   0.00-10.00  sec  11.2 GBytes  9.61 Gbits/sec

Hostinger actually responded with proper tuning guide. Decent disk IO, meh network before fix, good network after.

Comparison:
- GreenCloudVPS: no guidance, stock ancient kernel
- Leaseweb: auto-tuned, no issue
- Time4VPS: "upgrade to dedicated NIC" ($$$)
- Hostinger: https://hostinger.com/kb/irq-tuning (proper)

Numbers don't lie. Most providers don't either, they just don't know.

Right then, @SingaporeRep — cheers lads, we try. Proper network tuning shouldn't be a paid upgrade, it's just... proper. Our virtio driver has xps/rps on by default since 2024. Old boxes still need manual kick though.

Honest limits: if you're on our legacy KVM stack (pre-2023), irq affinity is manual. New stack handles it. Can check which you're on in panel. Not hiding it, just haven't migrated everyone yet.

@pablo if you want to patch virtio yourself on GreenCloudVPS, I'd... not. Their ToS is twitchy about "unauthorized modification."

GreenCloudVPS doesn't. Hostinger does but KYC for crypto is annoying. RackNerd takes XMR no questions, anyone know their virtio situation? Would rather pay in privacy coins than hand over passport for a VPS

Also @pablo be careful with that patch bro. "unauthorized modification" is vague on purpose

Which kernel version is GreenCloudVPS running exactly