From: Vladimir Davydov Date: Sun, 15 Sep 2013 13:49:13 +0000 (+0400) Subject: sched/balancing: Fix 'local->avg_load > sds->avg_load' case in calculate_imbalance() X-Git-Tag: v3.12-rc3~29^2~2 X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=b18855500fc40da050512d9df82d2f1471e59642;p=pandora-kernel.git sched/balancing: Fix 'local->avg_load > sds->avg_load' case in calculate_imbalance() In busiest->group_imb case we can come to calculate_imbalance() with local->avg_load >= busiest->avg_load >= sds->avg_load. This can result in imbalance overflow, because it is calculated as follows env->imbalance = min( max_pull * busiest->group_power, (sds->avg_load - local->avg_load) * local->group_power) / SCHED_POWER_SCALE; As a result we can end up constantly bouncing tasks from one cpu to another if there are pinned tasks. Fix this by skipping the assignment and assuming imbalance=0 in case local->avg_load > sds->avg_load. [ The bug can be caught by running 2*N cpuhogs pinned to two logical cpus belonging to different cores on an HT-enabled machine with N logical cpus: just look at se.nr_migrations growth. ] Signed-off-by: Vladimir Davydov Signed-off-by: Peter Zijlstra Link: http://lkml.kernel.org/r/8f596cc6bc0e5e655119dc892c9bfcad26e971f4.1379252740.git.vdavydov@parallels.com Signed-off-by: Ingo Molnar --- Reading git-diff-tree failed