On Mon, Jan 13, 2014 at 01:22:40PM +0530, Preeti Murthy wrote: > Hi, > > On Mon, Jan 6, 2014 at 5:09 PM, Mel Gorman <mgor...@suse.de> wrote: > > (Rik, you authored this patch so it should be sent from you and needs a > > signed-off assuming people are ok with the changelog.) > > > > Thomas Hellstrom bisected a regression where erratic 3D performance is > > experienced on virtual machines as measured by glxgears. It identified > > commit 58d081b5 (sched/numa: Avoid overloading CPUs on a preferred NUMA > > node) as the problem which had modified the behaviour of effective_load. > > > > Effective load calculates the difference to the system-wide load if a > > scheduling entity was moved to another CPU. The task group is not heavier > > as a result of the move but overall system load can increase/decrease as a > > result of the change. Commit 58d081b5 (sched/numa: Avoid overloading CPUs > > on a preferred NUMA node) changed effective_load to make it suitable for > > calculating if a particular NUMA node was compute overloaded. To reduce > > the cost of the function, it assumed that a current sched entity weight > > of 0 was uninteresting but that is not the case. > > > > wake_affine uses a weight of 0 for sync wakeups on the grounds that it > > is assuming the waking task will sleep and not contribute to load in the > > near future. In this case, we still want to calculate the effective load > > of the sched entity hierarchy. As effective_load is no longer used by > > Would it be worth mentioning that besides sync wakeups, wake_affine() uses a > weight of 0 for the sched entity, for effective load calculation on > the prev_cpu as well? > This is so as to find the effect of moving this task away from the > prev_cpu. Here > too we are interested in calculating the effective load of the root > task group of this > sched entity on the prev_cpu and the below restored check will be relevant. > > Without the below check the difference in the loads of the wake affine > CPU and the > prev_cpu can get messed up. >
I was too slow getting to this mail unfortunately. The patch is already merged upstream with the changelog as-is. -- Mel Gorman SUSE Labs -- 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/
