Re: [Qemu-devel] Using virtio-net and vhost_net on an ARM machine using qemu-system-arm & KVM

[Ying-Shiuan Pan <yingshiuan.pan@gmail.com>]

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Hi, Barak,

Hope the following info can help you

1.
HOST:
 <http://git.linaro.org/people/christoffer.dall/linux-kvm-arm.git>
http://git.linaro.org/people/christoffer.dall/linux-kvm-arm.git
branch: v3.10-arndale
config: arch/arm/configs/exynos5_arndale_defconfig
dtb: arch/arm/boot/dts/exynos5250-arndale.dtb
rootfs: Ubuntu 13.10

GUEST:
Official 3.12
config: arch/arm/configs/vexpress_defconfig  with virtio-devices enabled
dtb: arch/arm/boot/dts/vexpress-v2p-ca15-tc1.dtb
rootfs: Ubuntu 12.04

2.
We are still developing it in progress and will try to open source asap.
The main purpose of that patch is to introduce the ioeventfd into kvm-arm

3. as mentioned in 1.

4. qemu-1.6.0

5. We ported part of guest/host notifiers of virtio-pci to virtio-mmio

6. /usr/bin/qemu-system-arm -enable-kvm -kernel /root/nfs/zImage -m 128
--machine vexpress-a15 -cpu cortex-a15 -drive
file=/root/nfs/guest-1G-precise-vm1.img,id=virtio-blk,if=none,cache=none
-device virtio-blk-device,drive=virtio-blk -append "earlyprintk=ttyAMA0
console=ttyAMA0 root=/dev/vda rw ip=192.168.101.101::192.168.101.1:vm1:eth0:off
--no-log" -dtb /root/nfs/vexpress-v2p-ca15-tc1.dtb --nographic -chardev
socket,id=mon,path=/root/vm1.monitor,server,nowait -mon
chardev=mon,id=monitor,mode=readline -device
virtio-net-device,netdev=net0,mac="52:54:00:12:34:01" -netdev
type=tap,id=net0,script=/root/nfs/net.sh,downscript=no,vhost=off

vhost-net could be truned on by changing the last parameter vhost=on.

--
Ying-Shiuan Pan,
H Div., CCMA, ITRI, TW


----
Best Regards,
潘穎軒Ying-Shiuan Pan


2014/1/13 Barak Wasserstrom <wbarak@gmail.com>

> Ying-Shiuan Pan,
> Your experiments with arndale Exynos-5250 board can help me greatly and i
> would really appreciate if you share with me the following information:
> 1. Which Linux kernel did you use for the host and for the guest?
> 2. Which Linux kernel patches did you use for KVM?
> 3. Which config files did you use for both the host and guest?
> 4. Which QEMU did you use?
> 5. Which QEMU patches did you use?
> 6. What is the exact command line you used for invoking the guest, with
> and without vhost-net?
>
> Many thanks in advance!
>
> Regards,
> Barak
>
>
>
> On Mon, Jan 13, 2014 at 5:47 AM, Ying-Shiuan Pan <yingshiuan.pan@gmail.com
> > wrote:
>
>> Hi, Barak,
>>
>> We've tried vhost-net in kvm-arm on arndale Exynos-5250 board (it
>> requires some patches in qemu and kvm, of course). It works (without irqfd
>> support), however, the performance does not increase much. The throughput
>> (iperf) of virtio-net and vhost-net are 93.5Mbps and 93.6Mbps respectively.
>> I thought the result are because both virtio-net and vhost-net almost
>> reached the limitation of 100Mbps Ethernet.
>>
>> The good news is that we even ported vhost-net in our kvm-a9 hypervisor
>> (refer:
>> http://academic.odysci.com/article/1010113020064758/evaluation-of-a-server-grade-software-only-arm-hypervisor),
>> and the throughput of vhost-net on that platform (with 1Gbps Ethernet)
>> increased from 323Mbps to 435Mbps.
>>
>> --
>> Ying-Shiuan Pan,
>> H Div., CCMA, ITRI, TW
>>
>>
>> ----
>> Best Regards,
>> 潘穎軒Ying-Shiuan Pan
>>
>>
>> 2014/1/13 Peter Maydell <peter.maydell@linaro.org>
>>
>>> On 12 January 2014 21:49, Barak Wasserstrom <wbarak@gmail.com> wrote:
>>> > Thanks - I got virtio-net-device running now, but performance is
>>> terrible.
>>> > When i look at the guest's ethernet interface features (ethtool -k
>>> eth0) i
>>> > see all offload features are disabled.
>>> > I'm using a virtual tap on the host (tap0 bridged to eth3).
>>> > On the tap i also see all offload features are disabled, while on br0
>>> and
>>> > eth3 i see the expected offload features.
>>> > Can this explain the terrible performance i'm facing?
>>> > If so, how can this be changed?
>>> > If not, what else can cause such bad performance?
>>> > Do you know if vhost_net can be used on ARM Cortex A15 host/guest, even
>>> > though the guest doesn't support PCI & MSIX?
>>>
>>> I have no idea, I'm afraid. I don't have enough time available to
>>> investigate performance issues at the moment; if you find anything
>>> specific you can submit patches...
>>>
>>> thanks
>>> -- PMM
>>>
>>>
>>
>

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