Messages in this thread Patch in this message | | | From | Qais Yousef <> | Subject | [PATCH v3 2/6] sched/rt: Re-instate old behavior in select_task_rq_rt | Date | Mon, 2 Mar 2020 13:27:17 +0000 |
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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.
Reported-by: Pavan Kondeti <pkondeti@codeaurora.org> Fixes: 804d402fb6f6 ("sched/rt: Make RT capacity-aware") LINK: https://lore.kernel.org/lkml/20200218041620.GD28029@codeaurora.org/ Signed-off-by: Qais Yousef <qais.yousef@arm.com> ---
Notes: Changes since v2: * Check that target != -1 (thanks Dietmar)
kernel/sched/rt.c | 9 +++++++++ 1 file changed, 9 insertions(+)
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c index 4043abe45459..0afc70c9b68b 100644 --- a/kernel/sched/rt.c +++ b/kernel/sched/rt.c @@ -1474,6 +1474,13 @@ 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. @@ -1482,6 +1489,8 @@ 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: -- 2.17.1
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