On Fri, Nov 8, 2019 at 7:56 PM Ferruh Yigit <ferruh.yi...@intel.com> wrote: > > > >> Hi Vasim, Jerin, > >> > >> Overall looks good and I not getting any functional error but I am > >> observing a > >> huge performance drop with this update, 3.8Mpps to 0.7Mpps [1]. > > > > Hi Ferruh, > > When it comes to actual kernel netdev test cases like iperf or any other > > use cases, there would not be any impact on performance. I think synthetic > > test case like loopback mode might not be the actual test case alone to > > depend on when the kernel module is featured to work with kind of > > devices(pdev or vdev). Users can always fallback to pa mode with cmd line > > option. > > > > Please suggest your thoughts on considering what test case to use & > > evaluate the performance difference. > > Hi Vasim, > > I also assume the real life test cases will be affected less, but the loopback > performance testing is good to show performance impact of the change.
Yes. real-world case Linux kernel stack will be the bottleneck. > > (Stephen's predictions that KNI is not as fast as tun/tap are getting more > real > by time J) > > At least I think the possible performance drop and how to mitigate it should > be > documented both in release notes and kni documentation. +1 for adding documentation. Setting iova-mode=pa will be mitigation if the application does not care about iova-mode. > > For the final decision, I am not objecting it but I would like to see more ack > from community to confirm that we trade off iova=va functionality against > performance. In my view, IOVA as VA mode case, translation cannot be avoided and we have the requirement where it needs to work with vdev(where is not backed by any IOMMU context) so I am not sure how to avoid the translation cost. Since we have support for both modes,i.e existing IOVA as PA path still exists, I don't think, we are losing anything. > @Jerin, @Thomas, should we conclude this in techboard? Perhaps we can get it > for > rc2 and drop it back if rejected in techboard? > > Regards, > ferruh
