Re: [REPORT] cfs-v4 vs sd-0.44

[Ingo Molnar <mingo@elte.hu>]

* Linus Torvalds <torvalds@linux-foundation.org> wrote:

> It would be even better to simply have the rule:
>  - child gets almost no points at startup
>  - but when a parent does a "waitpid()" call and blocks, it will spread 
>    out its points to the childred (the "vfork()" blocking is another case 
>    that is really the same).
> 
> This is a very special kind of "priority inversion" logic: you give 
> higher priority to the things you wait for. Not because of holding any 
> locks, but simply because a blockign waitpid really is a damn big hint 
> that "ok, the child now works for the parent".

yeah. One problem i can see with the implementation of this though is 
that shells typically do nonspecific waits - for example bash does this 
on a simple 'ls' command:

  21310 clone(child_stack=0,  ...) = 21399
  ...
  21399 execve("/bin/ls", 
  ...
  21310 waitpid(-1, <unfinished ...>

the PID is -1 so we dont actually know which task we are waiting for. We 
could use the first entry from the p->children list, but that looks too 
specific of a hack to me. It should catch most of the 
synchronous-helper-task cases though.

	Ingo
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