On Wed, Sep 26, 2012 at 04:23:26AM +0200, Mike Galbraith wrote: > On Tue, 2012-09-25 at 20:42 +0200, Borislav Petkov wrote: > > > Right, so why did we need it all, in the first place? There has to be > > some reason for it. > > Easy. Take two communicating tasks. Is an affine wakeup a good idea? > It depends on how much execution overlap there is. Wake affine when > there is overlap larger than cache miss cost, and you just tossed > throughput into the bin. > > select_idle_sibling() was originally about shared L2, where any overlap > was salvageable. On modern processors with no shared L2,
Oh, but we do have shared L2s in the Bulldozer uarch (a subset of the modern AMD processors :)). > you have to get past the cost, but the gain is still there. Intel > wins with loads that AMD loses very bady on, so I can only guess that > Intel must feed caches more efficiently. Dunno. It just doesn't matter > though, point is that there is a win to be had in both cases, the > breakeven just isn't at the same point. Well, I guess selecting the proper core in the hierarchy depending on the workload is one of those hard problems. Teaching select_idle_sibling to detect the breakeven point and act accordingly would be not that easy then... Thanks. -- Regards/Gruss, Boris. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
