sched/fair: Take the scheduling domain into account in select_idle_smt()

When picking a CPU on task wakeup, select_idle_smt() has to take
into account the scheduling domain of @target. This is because the
"isolcpus" kernel command line option can remove CPUs from the domain to
isolate them from other SMT siblings.

This fix checks if the candidate CPU is in the target scheduling domain.

Commit:

  df3cb4ea1fb6 ("sched/fair: Fix wrong cpu selecting from isolated domain")

... originally introduced this fix by adding the check of the scheduling
domain in the loop.

However, commit:

  3e6efe87cd5cc ("sched/fair: Remove redundant check in select_idle_smt()")

... accidentally removed the check. Bring it back.

Fixes: 3e6efe87cd5c ("sched/fair: Remove redundant check in select_idle_smt()")
Signed-off-by: Keisuke Nishimura <keisuke.nishimura@inria.fr>
Signed-off-by: Julia Lawall <julia.lawall@inria.fr>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Link: https://lore.kernel.org/r/20240110131707.437301-1-keisuke.nishimura@inria.fr

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index ba3633940f6fc470272790349944385739e71c4a..005f6d31e8f6be09325cde8c4fedf2c8801dd496 100644 (file)
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -7311,13 +7311,19 @@ static int select_idle_core(struct task_struct *p, int core, struct cpumask *cpu
 /*
  * Scan the local SMT mask for idle CPUs.
  */
-static int select_idle_smt(struct task_struct *p, int target)
+static int select_idle_smt(struct task_struct *p, struct sched_domain *sd, int target)
 {
        int cpu;
 
        for_each_cpu_and(cpu, cpu_smt_mask(target), p->cpus_ptr) {
                if (cpu == target)
                        continue;
+               /*
+                * Check if the CPU is in the LLC scheduling domain of @target.
+                * Due to isolcpus, there is no guarantee that all the siblings are in the domain.
+                */
+               if (!cpumask_test_cpu(cpu, sched_domain_span(sd)))
+                       continue;
                if (available_idle_cpu(cpu) || sched_idle_cpu(cpu))
                        return cpu;
        }
@@ -7341,7 +7347,7 @@ static inline int select_idle_core(struct task_struct *p, int core, struct cpuma
        return __select_idle_cpu(core, p);
 }
 
-static inline int select_idle_smt(struct task_struct *p, int target)
+static inline int select_idle_smt(struct task_struct *p, struct sched_domain *sd, int target)
 {
        return -1;
 }
@@ -7591,7 +7597,7 @@ static int select_idle_sibling(struct task_struct *p, int prev, int target)
                has_idle_core = test_idle_cores(target);
 
                if (!has_idle_core && cpus_share_cache(prev, target)) {
-                       i = select_idle_smt(p, prev);
+                       i = select_idle_smt(p, sd, prev);
                        if ((unsigned int)i < nr_cpumask_bits)
                                return i;
                }