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

Ingo Molnar
2007-04-21T16:54:39Z

* 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