Hi, I totally agree with Avi's comments. This topic is really important for the future of DPDK. So I think we must give some time to continue the discussion and have netdev involved in the choices done. As a consequence, these series should not be merged in the release 16.04. Thanks for continuing the work.
2016-02-29 12:58, Avi Kivity: > On 02/29/2016 12:43 PM, Ferruh Yigit wrote: > > On 2/29/2016 9:43 AM, Avi Kivity wrote: > >> On 02/28/2016 10:16 PM, Ferruh Yigit wrote: > >>> On 2/28/2016 3:34 PM, Avi Kivity wrote: > >>>> On 01/27/2016 06:24 PM, Ferruh Yigit wrote: > >>>>> This kernel module is based on KNI module, but this one is stripped > >>>>> version of it and only for control messages, no data transfer > >>>>> functionality provided. > >>>>> > >>>>> This Linux kernel module helps userspace application create virtual > >>>>> interfaces and when a control command issued into that virtual > >>>>> interface, module pushes the command to the userspace and gets the > >>>>> response back for the caller application. > >>>>> > >>>>> The Linux tools like ethtool/ifconfig/ip can be used on virtual > >>>>> interfaces but not ones for related data, like tcpdump. > >>>>> > >>>>> In long term this patch intends to replace the KNI and KNI will be > >>>>> depreciated. > >>>> Instead of adding yet another out-of-tree kernel module, why not extend > >>>> the existing in-tree tap driver? This will make everyone's life easier. > >>>> > >>>> Since tap also supports data transfer, an application can also forward > >>>> packets not intended to it to the kernel, and forward packets from the > >>>> kernel through the device. > >>>> > >>> Hi Avi, > >>> > >>> KDP (Kernel Data Path) does what you have described, it is implemented > >>> as PMD and it benefits from tap driver to data transfer through the > >>> kernel. It also support custom kernel module for better performance. > >>> > >>> For KCP (Kernel Control Path), network driver forwards control commands > >>> to the userspace driver, I doubt this is something wanted for tun/tap > >>> driver, so extending tun/tap driver like this can be hard to upstream. > >> Have you tried asking? Maybe if you explain it they will be open to the > >> extension. > >> > > Not communicated but tun/tap already doing something different. > > For KCP, created interface is map of the DPDK port. All data interface > > shows coming from DPDK port. For example if you get stats information > > with ifconfig, the values you observe are DPDK port statistics -not > > statistics of data between userspace and kernelspace, statistics of data > > forwarded between DPDK ports. If you down the interface, DPDK port > > stopped, etc... > > > > If you extend the tun/tap, it won't be map of the DPDK port, and if you > > get statistics information from that interface, what do you expect to > > see, the data transferred between kernel and userspace, or underlying > > DPDK port forwarding statistics? > > Good point. But you really have to involve netdev on this, or you'll > live out-of-tree forever. +1 > > Extending tun/tap in a way we want, forwarding all control commands to > > userspace, will break the current tun/tap, this doesn't looks like a > > valid option to me. > > It's possible to enhance it while preserving backwards compatibility, by > enabling a feature flag (statistics from userspace). +1 > > For data path, using tun/tap is OK and we are already doing it, for the > > control path I believe we need a new driver. > > > >> Certainly it will be better to have KCP and KDP use the same kernel > >> interface name; so we'll need to either add data path support to kcp > >> (causing duplication with tap), or add control path support to tap. I > >> think the latter is preferable. > >> > > Why it is better to have same interface? Anyone who is not interested > > with kernel data path may want to control DPDK ports using common tools, > > or want to get some basic information and stats using ethtool or > > ifconfig. Why we need to bind two different functionality together? > > Having two interfaces will be confusing for the user. If I wish to > firewall data packets coming from the dpdk port, do I set firewall rules > on dpdk0 or tap0? +1 > I don't think it matters whether you extend tap, or add a data path to > kcp, but if you want to upstream it, it needs to be blessed by netdev. +1 > >>> We are investigating about adding a native support to Linux kernel for > >>> KCP, but there is no task started for this right now, any support is > >>> welcome.