On Tue, Mar 27, 2012 at 10:39:55AM +0200, Peter Zijlstra wrote: > You can talk pretty much anything down to O(1) that way. Take an > algorithm that is O(n) in the number of tasks, since you know you have a > pid-space constraint of 30bits you can never have more than 2^30 (aka > 1Gi) tasks, hence your algorithm is O(2^30) aka O(1). Still this O notation thingy... This is not about the max value but about the fact the number is _variable_ or _fixed_. If you have a variable amount of entries (and variable amount of memory) in a list it's O(N) where N is the number of entries (even if we know the max ram is maybe 4TB?). If you've a _fixed_ number of them it's O(1). Even if the fixed number is very large. It basically shows it won't degraded depending on load, and the cost per-schedule remains exactly fixed at all times (non liner cacheline and out-of-order CPU execution/HT effects aside). If it was O(N) the time this would take to run for each schedule shall have to vary at runtime depending on a some variable factor N and that's not the case here. You can argue about CPU hotplug though. But this is just math nitpicking because I already pointed out I agree the cacheline hits on a 1024 way would be measurable and needs fixing. I'm not sure how useful it is to keep arguing on the O notation when we agree on what shall be optimized in practice. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>