On Mon, Mar 04, 2019 at 04:42:32PM -0700, Jim Fehlig wrote: > Adding xen-devel to cc in case anyone there wants to comment on my latest > proposal... > > On 2/20/19 5:20 PM, Jim Fehlig wrote: > > There have been a few requests [1][2] to support Xen's max_grant_frames > > setting in libvirt domXML, but I'm not quite sure how to model it. The > > documentation [3] on this setting states: > > > > Specify the maximum number of grant frames the domain is allowed to have. This > > value controls how many pages the domain is able to grant access to for other > > domains, needed e.g. for the operation of paravirtualized devices. The default > > is settable via xl.conf(5). > > I've sent a patch to introduce an analogous default in the libvirt libxl driver > > https://www.redhat.com/archives/libvir-list/2019-March/msg00123.html > > > > > It smells of a <memtune> setting, e.g. the amount of memory a domain can > > share, but doesn't map to any of the existing settings. A new subelement > > <shared_limit> doesn't feel right. Does anyone suggest a better way of > > modeling max_grant_frames? > > After discussing the max_grant_frames setting a bit more with Juergen I had > the idea to model it as IO buffer space (or DMA space) of a xenbus > "controller". All PV devices in the guest connect to the xenbus controller > and make use of the available I/O buffer space. Guests with more PV devices > requiring more buffer can increase the space on the xenbus controller > device. > > One small wrinkle in this idea is that we currently don't model xenbus in > libvirt. I'd need to add support for a new xenbus controller type and start > implicitly creating it when creating guests with PV devices, similar to > auto-creation of controllers in the qemu driver. Also, there is no existing > controller setting for specifying buffer space. Perhaps a 'ram' attribute > could be added, similar to specifying memory for <video> devices? E.g. > > <controller type='xenbus' ram='256'/> > > Any opinion on this approach? Or other ideas for modeling this setting > in libvirt? Regardless of max grant frames support I think modeling xenbus as a <controller> is a reasonable thing to want to do. I don't have a preference on whether you call it "ram" or explicitly "maxGrantFrames" as an attribute. Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :| -- libvir-list mailing list libvir-list@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/libvir-list
