Re: [libvirt] hypervisor feature - hardware assisted paging

On 01/04/11 - 10:41:07AM, Jim Fehlig wrote: > I'm looking into a bug where a libvirt-created xen HVM guest boots > *very* slowly on an EPT-enabled machine, particularly when the guest has > a dedicated PCI device. > > xen-unstable c/s 16931 [1] introduced a per-guest HAP (hardware assisted > paging) setting. Unfortunately, the sane default of hap=1 is done by xm > client tool instead of xend, so an HVM guest created with xm tool > (hap=1) boots as expected but takes much longer when created through > libvirt (hap=0). > > Should libvirt expose this feature in domain XML? Should it be possible > to enable/disable hardware assisted paging on a per-guest level with > libvirt? If so, where does such a setting belong? It seems analogous > to enabling/disabling PAE and as such belongs under hypervisor > features. On IRC, Eric suggested it might fall under memoryBacking like > huge page support in KVM. > > If folks feel this setting should not be exposed, it could be > unconditionally set in the xen driver for HVM guests, similar to the way > usb setting is currently handled (see attached patch). Note that the > xen domain builder will ignore this setting on hardware without the feature. > My personal feeling is that this is something we should expose. It is useful for testing sometimes, so I think that we could expose it under the hypervisor features with apic, acpi, etc like you suggest.

However, I would caution you to beware adding the hap flag unconditionally.