From 118de48b5183dbb3d6281302528ad1a93624854f Mon Sep 17 00:00:00 2001 From: Suresh Siddha Date: Thu, 10 Feb 2011 10:23:28 +0100 Subject: sched: Use group weight, idle cpu metrics to fix imbalances during idle Commit: aae6d3ddd8b90f5b2c8d79a2b914d1706d124193 upstream Currently we consider a sched domain to be well balanced when the imbalance is less than the domain's imablance_pct. As the number of cores and threads are increasing, current values of imbalance_pct (for example 25% for a NUMA domain) are not enough to detect imbalances like: a) On a WSM-EP system (two sockets, each having 6 cores and 12 logical threads), 24 cpu-hogging tasks get scheduled as 13 on one socket and 11 on another socket. Leading to an idle HT cpu. b) On a hypothetial 2 socket NHM-EX system (each socket having 8 cores and 16 logical threads), 16 cpu-hogging tasks can get scheduled as 9 on one socket and 7 on another socket. Leaving one core in a socket idle whereas in another socket we have a core having both its HT siblings busy. While this issue can be fixed by decreasing the domain's imbalance_pct (by making it a function of number of logical cpus in the domain), it can potentially cause more task migrations across sched groups in an overloaded case. Fix this by using imbalance_pct only during newly_idle and busy load balancing. And during idle load balancing, check if there is an imbalance in number of idle cpu's across the busiest and this sched_group or if the busiest group has more tasks than its weight that the idle cpu in this_group can pull. Reported-by: Nikhil Rao Signed-off-by: Suresh Siddha Signed-off-by: Peter Zijlstra Signed-off-by: Andi Kleen LKML-Reference: <1284760952.2676.11.camel@sbsiddha-MOBL3.sc.intel.com> Signed-off-by: Ingo Molnar Signed-off-by: Mike Galbraith Acked-by: Peter Zijlstra Signed-off-by: Greg Kroah-Hartman --- include/linux/sched.h | 1 + 1 file changed, 1 insertion(+) (limited to 'include') diff --git a/include/linux/sched.h b/include/linux/sched.h index 0c2e5b5d02cc..fc531a780124 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -856,6 +856,7 @@ struct sched_group { * single CPU. */ unsigned int cpu_power; + unsigned int group_weight; /* * The CPUs this group covers. -- cgit v1.2.3