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

Kyle Moffett
2007-04-21T18:56:27Z

On Apr 21, 2007, at 12:42:41, William Lee Irwin III wrote:
> On Sat, 21 Apr 2007, Willy Tarreau wrote:
>>> If you remember, with 50/50, I noticed some difficulties to fork
>>> many processes. I think that during a fork(), the parent has a
>>> higher probability of forking other processes than the child. So
>>> at least, we should use something like 67/33 or 75/25 for parent/
>>> child.
>
> On Sat, Apr 21, 2007 at 09:34:07AM -0700, Linus Torvalds 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".
>
> An in-kernel scheduler API might help. void yield_to(struct
> task_struct *)?
>
> A userspace API might be nice, too. e.g. int sched_yield_to(pid_t).

It might be nice if it was possible to actively contribute your CPU
time to a child process. For example:
int sched_donate(pid_t pid, struct timeval *time, int percentage);

Maybe a way to pass CPU time over a UNIX socket (analogous to
SCM_RIGHTS), along with information on what process/user passed it
That would make it possible to really fix X properly on a local
system. You could make the X client library pass CPU time to the X
server whenever it requests a CPU-intensive rendering operation.
Ordinarily X would nice all of its client service threads to +10, but
when a client passes CPU time to its thread over the socket, then its
service thread temporarily gets the scheduling properties of the
client. I'm not a scheduler guru, but that's what makes the most
sense from an application-programmer point of view.

Cheers,
Kyle Moffett