On Wed, Apr 18, 2007 at 07:48:21AM -0700, Linus Torvalds wrote: > > > On Wed, 18 Apr 2007, Matt Mackall wrote: > > > > Why is X special? Because it does work on behalf of other processes? > > Lots of things do this. Perhaps a scheduler should focus entirely on > > the implicit and directed wakeup matrix and optimizing that > > instead[1]. > > I 100% agree - the perfect scheduler would indeed take into account where > the wakeups come from, and try to "weigh" processes that help other > processes make progress more. That would naturally give server processes > more CPU power, because they help others > > I don't believe for a second that "fairness" means "give everybody the > same amount of CPU". That's a totally illogical measure of fairness. All > processes are _not_ created equal.
I believe that unless the kernel is told of these inequalities, then it must schedule fairly. And yes, by fairly, I mean fairly among all threads as a base resource class, because that's what Linux has always done (and if you aggregate into higher classes, you still need that per-thread scheduling). So I'm not excluding extra scheduling classes like per-process, per-user, but among any class of equal schedulable entities, fair scheduling is the only option because the alternative of unfairness is just insane. > That said, even trying to do "fairness by effective user ID" would > probably already do a lot. In a desktop environment, X would get as much > CPU time as the user processes, simply because it's in a different > protection domain (and that's really what "effective user ID" means: it's > not about "users", it's really about "protection domains"). > > And "fairness by euid" is probably a hell of a lot easier to do than > trying to figure out the wakeup matrix. Well my X server has an euid of root, which would mean my X clients can cause X to do work and eat into root's resources. Or as Ingo said, X may not be running as root. Seems like just another hack to try to implicitly solve the X problem and probably create a lot of others along the way. All fairness issues aside, in the context of keeping a very heavily loaded desktop interactive, X is special. That you are trying to think up funny rules that would implicitly give X better priority is kind of indicative of that. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
