[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] Disabling lapic and apic: pitfalls?
APIC is required for multiprocessor HVM guests. It can be lived without for UP guests. -- Keir On 14/3/08 17:55, "Dan Magenheimer" <dan.magenheimer@xxxxxxxxxx> wrote: > Excuse my newbie-ness in this area... I hope the answers aren't > too obvious or widely known. > > What are the disadvantages of disabling the LAPIC and APIC in a > Linux virtual machine? What functionality is lost? What class > of potential bugs might arise (or go away)? > > Does the answer differ for hvm vs pvm? > > Does the answer differ depending on whether the platform > underlying is Intel or AMD? 32-bit vs 64-bit? > > Does the answer differ for vcpus=1 vs vcpus>1 (assuming CONFIG_SMP) > > (And what about for Windows of various flavors?) > > For example, I can see that if lapic is enabled, an extra 1000 > interrupts per second are delivered to the VM (250 for pvm). > Are these useful for anything? Or are they just eating VM cycles? > > I suspect that disabled apic may break driver domains or pci > passthrough. True? What about lapic? > > I ask all these questions because I often see problem responses of > the type "Try apic=0" or "Boot with noapic" and I wonder about the > side effects of such a cure. Or whether the cure should be > universally applied for VMs: Depending on the answers to the > above questions, perhaps the default should be off and we > should be saying "Try apic=1 if you need that functionality". > > Thanks, > Dan > > > =================================== > If Xen could save time in a bottle / then clocks wouldn't virtually skew / > It would save every tick / for VMs that aren't quick / > and Xen then would send them anew > (with apologies to the late great Jim Croce) > _______________________________________________ > Xen-devel mailing list > Xen-devel@xxxxxxxxxxxxxxxxxxx > http://lists.xensource.com/xen-devel _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel
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