Oh yes, sorry for the ambiguity. I meant proposal to "park" unplugged vcpus. Thanks for the suggesting the practical approach. Anshul Makkar On Fri, Jun 6, 2014 at 3:36 PM, Gleb Natapov <gleb@xxxxxxxxxxxxx> wrote: > On Fri, Jun 06, 2014 at 03:02:59PM +0200, Anshul Makkar wrote: >> 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 ? >> > If by "above proposal" you mean the proposal in the email you linked, > then no since it tries to destroy vcpu, but does it incorrectly. If you > mean proposal to "park" unplugged vcpu, so that guest will not be able > to use it, then yes, it is pragmatic path forward. > > >> Thanks >> Anshul Makkar >> >> On Thu, May 29, 2014 at 10:12 AM, Gleb Natapov <gleb@xxxxxxxxxx> 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 majordomo@xxxxxxxxxxxxxxx >> > More majordomo info at http://vger.kernel.org/majordomo-info.html > > -- > Gleb. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
