Hi, On Mon, Mar 26, 2012 at 12:58:05PM -0700, Linus Torvalds wrote: > On Mar 26, 2012 12:45 PM, "Andrea Arcangeli" <aarcange@xxxxxxxxxx> wrote: > > > > As I wrote in the comment before the function, math speaking, this > > looks like O(N) but it is O(1), not O(N) nor O(N^2). This is because N > > = NR_CPUS = 1. > > That's just stupid sophistry. I agree, this is why I warned everyone in the comment before the function with the adjective "misleading": * O(1) misleading math * aside, the number of cachelines touched with thousands of CPU might * make it measurable. > No, you can't just say that it's limited to some large constant, and thus > the same as O(1). I pointed out it is O(1) just because if we use the O notation we may as well do the math right about it. I may not have been clear but I never meant that because it is O(1) (NR_CPUS constant) it means it's already ok as it is now. > > That's the worst kind of lie: something that's technically true if you look > at it a certain stupid way, but isn't actually true in practice. > > It's clearly O(n) in number of CPUs, and people told you it can't go into > the scheduler. Stop arguing idiotic things. Just say you'll fix it, instead > of looking like a tool. About fixing it, this can be called at a regular interval like load_balance() (which also has an higher cost than the per-cpu schedule fast path, in having to walk over the other CPU runqueues) or to be more integrated within CFS so it doesn't need to be called at all. I didn't think it was urgent to fix (also because it has a debug benefit to keep it like this in the short term), but I definitely intended to fix it. I also would welcome people who knows the scheduler so much better than me to rewrite or fix it as they like it. To be crystal clear: I totally agree to fix this, in the comment before the code I wrote: * it's good in the * short term for stressing the algorithm. I probably wasn't clear enough, but I already implicitly meant it shall be optimized further later. If there's a slight disagreement is only on the "urgency" to fix it but I will certainly change my priorities on this after reading your comments! Thanks for looking into this. Andrea -- 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>