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 majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html