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| author | Will Deacon <will@kernel.org> | 2021-07-30 14:24:28 +0300 |
|---|---|---|
| committer | Peter Zijlstra <peterz@infradead.org> | 2021-08-20 13:32:58 +0300 |
| commit | 9ae606bc74dd0e58d4de894e3c5cbb9d45599267 (patch) | |
| tree | d3459bdb6258212fb8e17196a3fb518c71afebca /kernel/sched | |
| parent | 304000390f88d049c85e9a0958ac5567f38816ee (diff) | |
| download | linux-9ae606bc74dd0e58d4de894e3c5cbb9d45599267.tar.xz | |
sched: Introduce task_cpu_possible_mask() to limit fallback rq selection
Asymmetric systems may not offer the same level of userspace ISA support
across all CPUs, meaning that some applications cannot be executed by
some CPUs. As a concrete example, upcoming arm64 big.LITTLE designs do
not feature support for 32-bit applications on both clusters.
On such a system, we must take care not to migrate a task to an
unsupported CPU when forcefully moving tasks in select_fallback_rq()
in response to a CPU hot-unplug operation.
Introduce a task_cpu_possible_mask() hook which, given a task argument,
allows an architecture to return a cpumask of CPUs that are capable of
executing that task. The default implementation returns the
cpu_possible_mask, since sane machines do not suffer from per-cpu ISA
limitations that affect scheduling. The new mask is used when selecting
the fallback runqueue as a last resort before forcing a migration to the
first active CPU.
Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Valentin Schneider <Valentin.Schneider@arm.com>
Reviewed-by: Quentin Perret <qperret@google.com>
Link: https://lore.kernel.org/r/20210730112443.23245-2-will@kernel.org
Diffstat (limited to 'kernel/sched')
| -rw-r--r-- | kernel/sched/core.c | 9 |
1 files changed, 3 insertions, 6 deletions
diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 7fa6ce74f40e..6f31267c4beb 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -2173,7 +2173,7 @@ static inline bool is_cpu_allowed(struct task_struct *p, int cpu) /* Non kernel threads are not allowed during either online or offline. */ if (!(p->flags & PF_KTHREAD)) - return cpu_active(cpu); + return cpu_active(cpu) && task_cpu_possible(cpu, p); /* KTHREAD_IS_PER_CPU is always allowed. */ if (kthread_is_per_cpu(p)) @@ -3124,9 +3124,7 @@ static int select_fallback_rq(int cpu, struct task_struct *p) /* Look for allowed, online CPU in same node. */ for_each_cpu(dest_cpu, nodemask) { - if (!cpu_active(dest_cpu)) - continue; - if (cpumask_test_cpu(dest_cpu, p->cpus_ptr)) + if (is_cpu_allowed(p, dest_cpu)) return dest_cpu; } } @@ -3156,10 +3154,9 @@ static int select_fallback_rq(int cpu, struct task_struct *p) * * More yuck to audit. */ - do_set_cpus_allowed(p, cpu_possible_mask); + do_set_cpus_allowed(p, task_cpu_possible_mask(p)); state = fail; break; - case fail: BUG(); break; |