On Sun, Mar 10, 2019 at 10:52:04AM +0200, Yuval Shaia wrote: > On Wed, Mar 06, 2019 at 12:39:17PM -0800, Bart Van Assche wrote: > > On Wed, 2019-03-06 at 22:14 +0200, Yuval Shaia wrote: > > > > > > > > > > > > > > > > > > > > > > > > > Suggestion: To enhance 'loopback' performances, can you consider > > > > > > > > > using shared memory or any other IPC instead of going thought > > > > > > > > > the > > > > > > > > > > > > > > network stack? > > > > > > > > > > > > > > > > > > > > > > > > > Loopback driver in this patchset doesn't use network stack. > > > > > > > > It is just 2000 lines of wrapper to memcpy() to enables > > > > > > > > applications to use > > > > > > > > > > > > > > rdma. > > > > > > > > > > > > > > To have a dedicated driver just for the loopback will force the user > > > > > > > to do a smart select, i.e. to use lo device for local traffic and rxe for non- > > > > > > > > > > local. > > > > > > No. when application is written using rdmacm, everything works based on > > > > > > > > > > the ip address. > > > > > > It will pick the right rdma device that matches this ip. > > > > > > It would be 'lo' when connections are on 127.0.0.1. > > > > > > When application such as MPI, will have to anyway specify the which rdma > > > > > > > > > > device they want to use in system. > > > > > > > > > > But what if one wants to stay at the verb level and not use rdmacm API? > > > > > > > > > > > > > Sure. He can stay at verb level where he anyway have to explicitly give the device name. > > > > > > And that's is exactly the problem! > > > > > > With qemu, the ibdev is given at the command-line of the virtual machine so > > > if two guests starts on the same host it is ok to give them the lo device > > > as backend but what will happen when one of the VMs will migrate to another > > > host? The traffic will break since the lo device cannot go outside. > > > > Hi Yuval, > > > > I think what you are describing falls outside the use cases Parav has in mind. I > > think that optimizing RDMA over loopback, even if that loopback only works inside > > a single VM, is useful. > > > > Bart. > > Sure, no argue here, just do not yet understood why not to optimize rxe and > enjoy both worlds? i.e. why to have new sw device just for loopback. > > We had this discussion in the past, recall Leon? What is the difference now? There is no difference now. RXE should and can be fixed/enhanced. Thanks > > Yuval
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