On 06/01/16 16:49, Jan Beulich wrote: >>>> On 06.01.16 at 17:38, <andrew.coop...@citrix.com> wrote: >> On 06/01/16 16:31, Jan Beulich wrote: >>>>>> On 06.01.16 at 15:44, <andrew.coop...@citrix.com> wrote: >>>> We did have an internal request for an HVM guest userspace netfront >>>> driver to be able to use evntchnop calls directly. >>> And this can't be accomplished using the evtchn and/or privcmd >>> drivers? >> It can, and I don't believe the worry about extra overhead is well >> placed. (There many areas of lower hanging fruit in this specific case). >> >> However, a userspace backend isn't in principle a bad idea. > Backend? Earlier you said frontend.
I did mean frontend, but it really doesn't matter as far as this is concerned. > Nor can I see how using the evtchn/privcmd devices would preclude that. They don't. I didn't imply that they would. > After all their purpose is to avoid having to expose hypercalls directly. Only one purpose. Another purpose is to enforce separation between processes, and handle allocation of global resources. In a dedicated utility VM, where all components are trusted, none of these reasons have as much weight as they do in a general purpose OS, and there is a valid argument to be made for favouring performance over isolation. I am not suggesting that userspace hypercalls would make orders of magnitude difference, but they would make some difference, and allow a Xen domain to have a more rDMA-like approach, if it chooses. ~Andrew _______________________________________________ Xen-devel mailing list Xen-devel@lists.xen.org http://lists.xen.org/xen-devel
