On Fri, Aug 03, 2007 at 01:10:13PM -0700, Suresh B wrote: > On Fri, Aug 03, 2007 at 02:20:10AM +0200, Nick Piggin wrote: > > On Thu, Aug 02, 2007 at 11:33:39AM -0700, Martin Bligh wrote: > > > Nick Piggin wrote: > > > >On Wed, Aug 01, 2007 at 03:52:11PM -0700, Martin Bligh wrote: > > > >>>And so forth. Initial forks will balance. If the children refuse to > > > >>>die, forks will continue to balance. If the parent starts seeing short > > > >>>lived children, fork()s will eventually start to stay local. > > > >>Fork without exec is much more rare than without. Optimising for > > > >>the uncommon case is the Wrong Thing to Do (tm). What we decided > > > > > > > >It's only the wrong thing to do if it hurts the common case too > > > >much. Considering we _already_ balance on exec, then adding another > > > >balance on fork is not going to introduce some order of magnitude > > > >problem -- at worst it would be 2x but it really isn't too slow > > > >anyway (at least nobody complained when we added it). > > > > > > > >One place where we found it helps is clone for threads. > > > > > > > >If we didn't do such a bad job at keeping tasks together with their > > > >local memory, then we might indeed reduce some of the balance-on-crap > > > >and increase the aggressiveness of periodic balancing. > > > > > > > >Considering we _already_ balance on fork/clone, I don't know what > > > >your argument is against this patch is? Doing the balance earlier > > > >and allocating more stuff on the local node is surely not a bad > > > >idea. > > > > > > I don't know who turned that on ;-( I suspect nobody bothered > > > actually measuring it at the time though, or used some crap > > > benchmark like stream to do so. It should get reverted. > > > > So you have numbers to show it hurts? I tested some things where it > > is not supposed to help, and it didn't make any difference. Nobody > > else noticed either. > > > > If the cost of doing the double balance is _really_ that painful, > > then we ccould skip balance-on-exec for domains with balance-on-fork > > set. > > Nick, Even if it is not painful, can we skip balance-on-exec if > balance-on-fork is set. There is no need for double balance, right?
I guess we could. There is no need for the double balance if the exec happens immediately after the fork which is surely the common case. I think there can be some other weird cases (eg multi-threaded code) that does funny things though... > Especially with the optimization you are trying to do with this patch, > balance-on-exec may lead to wrong decision making this optimization > not work as expected. That's true. - 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/
