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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----
Best Regards,
潘穎軒Ying-Shiuan Pan


2014/1/14 Barak Wasserstrom <wbarak@gmail.com>

> Ying-Shiuan Pan,
> Thanks again - please see few questions below.
>
> Regards,
> Barak
>
>
> On Tue, Jan 14, 2014 at 5:37 AM, Ying-Shiuan Pan <yingshiuan.pan@gmail.com
> > wrote:
>
>> 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
>>
> [Barak] Do you have any estimation about when you can release these
> patches?
>
Actually, No. I will discuss with my boss about the release plan.

>  [Barak] Is this required for enabling vhost-net?
>
Yes, it is because vhost-net relies on ioeventfd to get kick request from
front-end driver.


>
>>
>> 3. as mentioned in 1.
>>
>> 4. qemu-1.6.0
>>
>> 5. We ported part of guest/host notifiers of virtio-pci to virtio-mmio
>>
> [Barak] Any patches available for this?
>
I did not see any.. but there might be somebody is also developing this..

> [Barak] Is this required for enabling vhost-net?
>
Yes. Without those notifiers, you will see the error messages as you
mentioned below.

>
>
>>
>> 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
>>
> [Barak] Could you share "/root/nfs/net.sh" with me?
>
Sorry, I forgot that.
---------------
#!/bin/sh
ifconfig $1 0.0.0.0
brctl addif virbr0 $1
---------------

virbr0 is a bridge created by manual. The setup steps of virbr0 are also
provided:
brctl create virbr0
brctl addif virbr0 eth0
ifconfig virbr0 [ETH0_IP]
ifconfig eth0 0.0.0.0

[Barak] In the guest i can see that eth0 has all offload features disabled
> and cannot be enabled. I suspect this is related to the tap configuration
> in the host. Do you have any ideas?
>
>
>>
>> vhost-net could be truned on by changing the last parameter vhost=on.
>>
> [Barak] When enabling vhost i get errors in qemu, do you know what might
> be the reason?
> [Barak] qemu-system-arm: binding does not support guest notifiers
> [Barak] qemu-system-arm: unable to start vhost net: 38: falling back on
> userspace virtio
>
QEMU requires host/guest notifiers to setup vhost-net, but currently
virtio-mmio does not support yet.
That's why you got those error messages.

>
>
>>
>>
>> --
>> 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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