Paolo Bonzini wrote:
>>> 2) especially, the fix is not 100% safe unless I'm mistaken.
>>
>> What do you mean by "100% safe"? It is 100% deterministic (which is 
>> what I care about); I'm not sure what you mean when you use the term 
>> "safe" here.
> 
> It is not. 

Err, it is not what? Deterministic? Or safe? The point about it being 
deterministic did not relate to when exactly the process would resume 
(no real-time guarantee) but rather that it would resume 
deterministically in relation to its parent process (in this case, only 
after the parent process got suspended).

> Whether the low-priority process actually starts depends on 
> external factors.  If you have two priority-40 processes, they might 
> prevent the priority-39 process to start and resume the forked process. 

Correct. And it is an interesting question to discuss how the system 
*should* behave if it's exceeding its capabilities (i.e., running at 
100% CPU). But I'll leave that discussion for a different day.

Cheers,
   - Andreas