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| author | Qais Yousef <qais.yousef@arm.com> | 2020-03-02 13:27:17 +0000 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2020-03-06 12:57:27 +0100 |
| commit | b28bc1e002c23ff8a4999c4a2fb1d4d412bc6f5e (patch) | |
| tree | bf69a70331d7926ec74ddabb12ce119c5e4a82b2 /kernel/sched/rt.c | |
| parent | d9cb236b9429044dc694ea70a50163ddd283cea6 (diff) | |
| download | lwn-b28bc1e002c23ff8a4999c4a2fb1d4d412bc6f5e.tar.gz lwn-b28bc1e002c23ff8a4999c4a2fb1d4d412bc6f5e.zip | |
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.
LINK: https://lore.kernel.org/lkml/20200218041620.GD28029@codeaurora.org/
Reported-by: Pavan Kondeti <pkondeti@codeaurora.org>
Signed-off-by: Qais Yousef <qais.yousef@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Fixes: 804d402fb6f6 ("sched/rt: Make RT capacity-aware")
Link: https://lkml.kernel.org/r/20200302132721.8353-3-qais.yousef@arm.com
Diffstat (limited to 'kernel/sched/rt.c')
| -rw-r--r-- | kernel/sched/rt.c | 9 |
1 files changed, 9 insertions, 0 deletions
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c index 55a4a5042292..f0071fa01c1d 100644 --- a/kernel/sched/rt.c +++ b/kernel/sched/rt.c @@ -1475,6 +1475,13 @@ select_task_rq_rt(struct task_struct *p, int cpu, int sd_flag, int flags) 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: |