> -----Original Message-----
> From: Maxime Coquelin <[email protected]>
> Sent: Wednesday, April 15, 2020 10:16 PM
> To: Liu, Yong <[email protected]>; Ye, Xiaolong <[email protected]>;
> Wang, Zhihong <[email protected]>; [email protected]
> Cc: [email protected]
> Subject: Re: [PATCH] vhost: remove deferred shadow update
>
>
>
> On 4/1/20 11:29 PM, Marvin Liu wrote:
> > Defer shadow ring update will help overall throughput when frontend
> > much slower than backend. But that is not all the cases we faced now.
> > In case like ovs-dpdk + dpdk virtio user, frontend will much faster
> > than backend. Frontend may not be able to collect available descs when
> > shadow update is deferred. Thus will harm RFC2544 performance.
>
> I don't understand this comment. What is the difference in term of
> performance between Qemu + Virtio PMD and Virtio-User PMD, as the
> datapath is the same?
>
Hi Maxime,
The statement is for the different situations between virtio-net + vhost pmd
and virtio-user + vhost pmd in ovs.
When combination is virtio-user + vhost pmd in ovs, frontend will be much
faster than backend. Defer used ring update won't give benefit when requiring
zero packet loss.
Regards,
Marvin
> > Solution is just remove deferred shadow update, which will help RFC2544
> > and fix potential issue with virtio net driver.
>
> What is the potential issue?
>
> Maxime
It is napi stops issue which has been fixed by Eugenio.
