On 25/09/2018 10:57, Roman Kagan wrote: > Speaking of the options we have, the choice depends on the assumptions > we take. (And I guess when you spoke of quadratic complexity you > referred to the algorithm to convert the vp_index mask into the KVM cpu > mask.) Right; with Vitaly's patch, if you have a random mapping between vp_index and cpu index, each loop requires a list walk, and so you have O(#VMcpus * #IPIcpus) worst case for sending an IPI to #IPIcpus CPUs in a guest with #VMcpus. > If we can assume that in all relevant cases vp_index coincides with the > cpu index (which I think we can) then Vitaly's approach is the most > efficient. > > If, on the opposite, we want to optimize for random mapping between > vp_index and cpu index, then it's probably better instead to iterate > over vcpus and test if their vp_index belongs to the requested mask. Yes, that would work too. Perhaps we can do both? You can have a kvm->num_mismatched_vp_indexes count to choose between the two. Paolo > Neither of the above is quadratic. > Dunno if we need to specifically consider intermediate situations.
