IIRC, Igor was of the opinion that patch for vcpu deletion will be incomplete till its handled properly in kvm i.e vcpus are destroyed completely. http://comments.gmane.org/gmane.comp.emulators.kvm.devel/114347 .
So can the above proposal where just vcpus can be disabled and reused in qemu is an acceptable solution ? Thanks Anshul Makkar On Thu, May 29, 2014 at 10:12 AM, Gleb Natapov <[email protected]> wrote: > On Thu, May 29, 2014 at 01:40:08PM +0800, Gu Zheng wrote: >> >> There was a patch(from Chen Fan, last august) about releasing vcpu when >> >> closing vcpu fd <http://www.spinics.net/lists/kvm/msg95701.html>, but >> >> your comment said "Attempt where made to make it possible to destroy >> >> individual vcpus separately from destroying VM before, but they were >> >> unsuccessful thus far." >> >> So what is the pain here? If we want to achieve the goal, what should we >> >> do? >> >> Looking forward to your further comments.:) >> >> >> > CPU array is accessed locklessly in a lot of places, so it will have to be >> > RCUified. >> > There was attempt to do so 2 year or so ago, but it didn't go anyware. >> > Adding locks is >> > to big a price to pay for ability to free a little bit of memory by >> > destroying vcpu. >> >> Yes, it's a pain here. But if we want to implement "vcpu hot-remove", this >> must be >> fixed sooner or later. > Why? "vcpu hot-remove" already works (or at least worked in the past > for some value of "work"). No need to destroy vcpu completely, just > park it and tell a guest not to use it via ACPI hot unplug event. > >> And any guys working on kvm "vcpu hot-remove" now? >> >> > An >> > alternative may be to make sure that stopped vcpu takes as little memory >> > as possible. >> >> Yeah. But if we add a new vcpu with the old id that we stopped before, it >> will fail. >> > No need to create vcpu again, just unpark it and notify a guest via ACPI hot > plug event that > vcpu can be used now. > > -- > Gleb. > -- > To unsubscribe from this list: send the line "unsubscribe kvm" in > the body of a message to [email protected] > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
