netdev - Re: provide vhost thread per virtqueue for forwarding scenario

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Date:	Thu, 23 May 2013 13:43:29 +0930
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Jason Wang <jasowang@...hat.com>,
	Zang Hongyong <zanghongyong@...wei.com>
Cc:	"Michael S. Tsirkin" <mst@...hat.com>,
	Qinchuanyu <qinchuanyu@...wei.com>,
	"nab\@linux-iscsi.org" <nab@...ux-iscsi.org>,
	"\(netdev\@vger.kernel.org\)" <netdev@...r.kernel.org>,
	"\(kvm\@vger.kernel.org\)" <kvm@...r.kernel.org>,
	"Zhangjie \(HZ\)" <zhang.zhangjie@...wei.com>
Subject: Re: provide vhost thread per virtqueue for forwarding scenario

Jason Wang <jasowang@...hat.com> writes:
> On 05/22/2013 05:59 PM, Zang Hongyong wrote:
>> On 2013/5/20 15:43, Michael S. Tsirkin wrote:
>>> On Mon, May 20, 2013 at 02:11:19AM +0000, Qinchuanyu wrote:
>>> Yes, I don't think we want to create threads even more aggressively
>>> in all cases. I'm worried about scalability as it is.
>>> I think we should explore a flexible approach, use a thread pool
>>> (for example, a wq) to share threads between virtqueues,
>>> switch to a separate thread only if there's free CPU and existing
>>> threads are busy. Hopefully share threads between vhost instances too.
>> On Xen platform, network backend pv driver model has evolved to this
>> way. Netbacks from all DomUs share a thread pool,
>> and thread number eaqual to cpu core number.
>> Is there any plan for kvm paltform?
>
> There used to be two related RFCs for this, one is the multiple vhost
> workers from Anthony another is percpu vhost thread from Shirley. You
> can search the archives on netdev or kvm for the patches.

As I've said to MST before, I think our entire model is wrong.
Userspace should create the threads and call in.  If you're doing kernel
acceleration, two extra threads per NIC is a tiny overhead.

Of course, such radical changes to vhost doesn't help existing users as
Qinchuanyu asked...

Cheers,
Rusty,
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