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
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