Re: [RFC PATCH for 4.21 03/16] sched: Implement push_task_to_cpu (v2)
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From: Srikar Dronamraju <hidden>
Date: 2018-10-17 06:52:03
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lkml
Hi Mathieu,
+int push_task_to_cpu(struct task_struct *p, unsigned int dest_cpu)
+{
In your use case, is the task going to be current?
If yes, we should simply be using migrate_task_to.
quoted hunk ↗ jump to hunk
+ struct rq_flags rf; + struct rq *rq; + int ret = 0; + + rq = task_rq_lock(p, &rf); + update_rq_clock(rq); + + if (!cpumask_test_cpu(dest_cpu, &p->cpus_allowed)) { + ret = -EINVAL; + goto out; + }
Ideally we should have checked cpus_allowed/cpu_active_mask before taking
the lock. This would help reduce the contention on the rqlock when the
passed parameter is not correct.
quoted hunk ↗ jump to hunk
+ + if (!cpumask_test_cpu(dest_cpu, cpu_active_mask)) { + ret = -EBUSY; + goto out; + } + + if (task_cpu(p) == dest_cpu) + goto out;
Same as above.
+
+ if (task_running(rq, p) || p->state == TASK_WAKING) {Why are we using migration thread to move a task in TASK_WAKING state?
quoted hunk ↗ jump to hunk
+ struct migration_arg arg = { p, dest_cpu }; + /* Need help from migration thread: drop lock and wait. */ + task_rq_unlock(rq, p, &rf); + stop_one_cpu(cpu_of(rq), migration_cpu_stop, &arg); + tlb_migrate_finish(p->mm); + return 0;
Why cant we use migrate_task_to instead?
quoted hunk ↗ jump to hunk
+ } else if (task_on_rq_queued(p)) {diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index 455fa330de04..27ad25780204 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h@@ -1340,6 +1340,15 @@ static inline void __set_task_cpu(struct task_struct *p, unsigned int cpu) #endif } +#ifdef CONFIG_SMP +int push_task_to_cpu(struct task_struct *p, unsigned int dest_cpu); +#else +static inline int push_task_to_cpu(struct task_struct *p, unsigned int dest_cpu) +{ + return 0; +} +#endif +
Your usecase is outside kernel/sched. So I am not sure if this is the right
place for the declaration.