From: Qin Chuanyu <qinchuanyu@huawei•com>
To: Anthony Liguori <anthony@codemonkey•ws>
Cc: "Michael S. Tsirkin" <mst@redhat•com>, <jasowang@redhat•com>,
KVM list <kvm@vger•kernel.org>, <netdev@vger•kernel.org>,
<qianhuibin@huawei•com>,
"xen-devel@lists•xen.org" <xen-devel@lists•xen.org>,
<wangfuhai@huawei•com>, <likunyun@huawei•com>,
<liuyongan@huawei•com>, <liuyingdong@huawei•com>
Subject: Re: Is fallback vhost_net to qemu for live migrate available？
Date: Sat, 31 Aug 2013 12:45:11 +0800 [thread overview]
Message-ID: <522174D7.6080903@huawei.com> (raw)
In-Reply-To: <CA+aC4kv66bvt5mREv-YXVddD9wdgAiT=heo9xhdkkVmuLOyrBw@mail.gmail.com>
On 2013/8/30 0:08, Anthony Liguori wrote:
> Hi Qin,
>> By change the memory copy and notify mechanism ，currently virtio-net with
>> vhost_net could run on Xen with good performance。
>
> I think the key in doing this would be to implement a property
> ioeventfd and irqfd interface in the driver domain kernel. Just
> hacking vhost_net with Xen specific knowledge would be pretty nasty
> IMHO.
>
Yes, I add a kernel module which persist virtio-net pio_addr and msix
address as what kvm module did. Guest wake up vhost thread by adding a
hook func in evtchn_interrupt.
> Did you modify the front end driver to do grant table mapping or is
> this all being done by mapping the domain's memory?
>
There is nothing changed in front end driver. Currently I use
alloc_vm_area to get address space， and map the domain's memory as what
what qemu did.
> KVM and Xen represent memory in a very different way. KVM can only
> track when guest mode code dirties memory. It relies on QEMU to track
> when guest memory is dirtied by QEMU. Since vhost is running outside
> of QEMU, vhost also needs to tell QEMU when it has dirtied memory.
>
> I don't think this is a problem with Xen though. I believe (although
> could be wrong) that Xen is able to track when either the domain or
> dom0 dirties memory.
>
> So I think you can simply ignore the dirty logging with vhost and it
> should Just Work.
>
Thanks for your advice, I have tried it, without ping, it could migrate
successfully, but if there has skb been received, domU would crash. I
guess that because though Xen track domU memory, but it could only track
memory that changed in DomU. memory changed by Dom0 is out of control.
>
> No, we don't have a mechanism to fallback to QEMU for the datapath.
> It would be possible but I think it's a bad idea to mix and match the
> two.
>
Next I would try to fallback datapath to qemu for three reason:
1: memory translate mechanism has been changed for vhost_net on Xen，so
there would be some necessary changed needed for vhost_log in kernel.
2: I also maped IOREQ_PFN page(which is used for communication between
qemu and Xen) in kernel notify module, so it also needed been marked as
dirty when tx/rx exist in migrate period.
3: Most important of all， Michael S. Tsirkin said that he hadn't
considered about vhost_net migrate on Xen，so there would be some
changed needed in vhost_log for qemu.
fallback to qemu seems to much easier, isn't it.
Regards
Qin chuanyu
next prev parent reply other threads:[~2013-08-31 4:45 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-08-27 3:32 Is fallback vhost_net to qemu for live migrate available？ Qin Chuanyu
2013-08-27 4:19 ` Michael S. Tsirkin
2013-08-27 7:04 ` Qin Chuanyu
2013-08-27 7:16 ` Michael S. Tsirkin
2013-08-27 7:22 ` Qin Chuanyu
2013-08-27 9:41 ` Wei Liu
2013-08-29 16:08 ` Anthony Liguori
2013-08-31 4:45 ` Qin Chuanyu [this message]
2013-09-02 3:19 ` Jason Wang
2013-09-02 7:57 ` Wei Liu
2013-09-02 8:11 ` Michael S. Tsirkin
2013-09-03 1:28 ` Qin Chuanyu
2013-09-03 8:40 ` Wei Liu
2013-09-03 8:55 ` Michael S. Tsirkin
2013-09-03 9:15 ` Wei Liu
2013-09-05 13:33 ` [Xen-devel] " Stefano Stabellini
2013-10-14 8:19 ` Qin Chuanyu
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