From 27d84b63b00318ab819cb680e2e5e570a889d667 Mon Sep 17 00:00:00 2001 From: Qais Yousef Date: Mon, 2 Mar 2020 13:27:17 +0000 Subject: [PATCH] FROMGIT: sched/rt: Re-instate old behavior in select_task_rq_rt() When RT Capacity Aware support was added, the logic in select_task_rq_rt was modified to force a search for a fitting CPU if the task currently doesn't run on one. But if the search failed, and the search was only triggered to fulfill the fitness request; we could end up selecting a new CPU unnecessarily. Fix this and re-instate the original behavior by ensuring we bail out in that case. This behavior change only affected asymmetric systems that are using util_clamp to implement capacity aware. None asymmetric systems weren't affected. Bug: 120440300 LINK: https://lore.kernel.org/lkml/20200218041620.GD28029@codeaurora.org/ Reported-by: Pavan Kondeti Signed-off-by: Qais Yousef Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Ingo Molnar Fixes: 804d402fb6f6 ("sched/rt: Make RT capacity-aware") Link: https://lkml.kernel.org/r/20200302132721.8353-3-qais.yousef@arm.com (cherry picked from commit b28bc1e002c23ff8a4999c4a2fb1d4d412bc6f5e https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git sched/core) Signed-off-by: Qais Yousef Change-Id: I670ab7f95a3bd8b4790e1cafe89308ead524367e --- kernel/sched/rt.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c index d94c4e319b9f..e7e192f7df47 100644 --- a/kernel/sched/rt.c +++ b/kernel/sched/rt.c @@ -1478,6 +1478,13 @@ select_task_rq_rt(struct task_struct *p, int cpu, int sd_flag, int flags, if (test || !rt_task_fits_capacity(p, cpu)) { int target = find_lowest_rq(p); + /* + * Bail out if we were forcing a migration to find a better + * fitting CPU but our search failed. + */ + if (!test && target != -1 && !rt_task_fits_capacity(p, target)) + goto out_unlock; + /* * Don't bother moving it if the destination CPU is * not running a lower priority task. @@ -1486,6 +1493,8 @@ select_task_rq_rt(struct task_struct *p, int cpu, int sd_flag, int flags, p->prio < cpu_rq(target)->rt.highest_prio.curr) cpu = target; } + +out_unlock: rcu_read_unlock(); out: