What I'm trying to do is isolate vCPUs on separate physical cores where pair siblings will be reserved / not used by any other VM nor by this VM as well. Of course it is about SMT/HT enabled hosts. So by using a combination of extra spec on flavor (cpu_policy=dedicated , plus thread_policy=isolate), i'm always receiving errors ( no host available) . I'm using the Victoria OpenStack release. 
I've found (also playing with AI tools) that this combination is tricky (buggy) in Victoria and might not work and it might always fail. 

Actually what this combination is introduced for ?