Re: Improving user networking performance

[Anders Pitman]

Hi Paul,

Thanks for the response. I've collected more precise data for you.

> Please share the command line, how you start the GNU/Linux VM, and what GNU/Linux distribution you use.

I'll share the specific command lines with the results data below. For the distro, I'm using buildroot-2022.02. I started with the configs/qemu_x86_64_defconfig file. Kernel 5.15.18. It's also set up to bundle the cpio initramfs inside the kernel image, includes iperf3, and e1000 drivers.

> Please be specific. What kind of laptop (CPU, …)?

It's an old Lenovo x220 laptop. Intel Core i5-2520M. 2 hyperthreaded cores. 2.5GHz. 8GB memory.

> How do you measure the transfer speed?

I'm using iperf3. It's running on the Windows 10 host using MSYS2, like so:

iperf3 -s

And from the guest like so:

iperf3 -c 10.0.2.2

Results:

As a baseline, I ran iperf3 over localhost on the host machine. Both client and server were running from MSYS2 with iperf3 installed using pacman -S iperf3. Results:

1.37Gbits/sec

For the remaining tests, I ran iperf from the guest to host like so:

iperf3 -c 10.0.2.2

qemu-system-x86_64.txt -kernel bzImage -append "console=ttyS0" -nic user,e1000

45.1Mbits/sec

qemu-system-x86_64.txt -kernel bzImage -append "console=ttyS0" -nic user,virtio

33.9Mbits/sec

qemu-system-x86_64.txt -kernel bzImage -append "console=ttyS0" -nic user,e1000 -accel whpx

63.5Mbits/sec

qemu-system-x86_64.txt -kernel bzImage -append "console=ttyS0" -nic user,virtio -accel whpx

83.4Mbits/sec

qemu-system-x86_64.txt -kernel bzImage -append "console=ttyS0" -nic user,virtio -accel whpx -m 4096 -smp 4

63.9Mbits/sec

Notes:

* virtio+whpx is the fastest, but virtio without whpx is slower than e1000.

* None of the tests are saturating the host CPU. In fact CPU usage according to Task Manager stays below ~20%.

* I get fairly different results from run to run for the same test. As much as +/- 10Mbits/sec observed so far.

* Apparently -cpu host doesn't work on Windows hosts?

Thanks again,

//anders

On Tue, Apr 5, 2022, at 11:44 PM, Paul Menzel wrote:

Dear Anders,

Am 05.04.22 um 22:31 schrieb Anders Pitman:

> I'm trying to improve user networking performance, especially from a

> Windows 10 host, Linux guest. My goal is to get at least 100Mbps

> duplex. I'm hoping to be able to saturate a 1Gbps link. I need to

> avoid requiring any admin privileges, which is why I'm doing user

> networking instead of setting up a TAP device.

Please share the command line, how you start the GNU/Linux VM, and what 

GNU/Linux distribution you use.

> Currently I'm seeing about 20-50Mbps on an older Windows 10 laptop.

Please be specific. What kind of laptop (CPU, …)?

How do you measure the transfer speed?

> Enabling -accel whpx improves that significantly, but still not

> 1Gbps, and requires Windows Pro and extra steps for the user to

> enable virtualization.

> 

> I have a few specific questions:

> 

> * Is 1Gbps realistic with my desired setup?

> * Does virtio work with the slirp user networking? I can enable it,

> but I'm not sure it's making much difference.

> * Is there potential to improve upon slirp with a different user

> networking implementation? It seems like if you set up an ivshmem

> interface (similar to how Looking Glass works) you could get really

> efficient packet transfers. I was under the impression this is how

> slirp+virtio would work, but again I'm not seeing the hoped-for

> performance.

> 

> If such a thing is possible but doesn't exist, I would be interested

> in working on it myself. I would appreciate any pointers on any

> additional resources to get started with this.

I’d say it should be possible with not-too old hardware, but I never 

tried it myself.

Kind regards,

Paul