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x86: kvm: Revert "remove sched notifier for cross-cpu migrations"

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The following point:

    2. per-CPU pvclock time info is updated if the
       underlying CPU changes.

Is not true anymore since "KVM: x86: update pvclock area conditionally,
on cpu migration".

Add task migration notification back.

Problem noticed by Andy Lutomirski.

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
CC: stable@kernel.org # 3.11+
This commit is contained in:
Marcelo Tosatti
2015-03-23 20:22:48 -03:00
parent 58d2930f4e
commit 0a4e6be9ca
5 changed files with 76 additions and 8 deletions
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kernel/sched/core.c
+15
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@@ -996,6 +996,13 @@ void check_preempt_curr(struct rq *rq, struct task_struct *p, int flags)
rq_clock_skip_update(rq, true);
}
static ATOMIC_NOTIFIER_HEAD(task_migration_notifier);
void register_task_migration_notifier(struct notifier_block *n)
{
atomic_notifier_chain_register(&task_migration_notifier, n);
}
#ifdef CONFIG_SMP
void set_task_cpu(struct task_struct *p, unsigned int new_cpu)
{
@@ -1026,10 +1033,18 @@ void set_task_cpu(struct task_struct *p, unsigned int new_cpu)
trace_sched_migrate_task(p, new_cpu);
if (task_cpu(p) != new_cpu) {
struct task_migration_notifier tmn;
if (p->sched_class->migrate_task_rq)
p->sched_class->migrate_task_rq(p, new_cpu);
p->se.nr_migrations++;
perf_sw_event_sched(PERF_COUNT_SW_CPU_MIGRATIONS, 1, 0);
tmn.task = p;
tmn.from_cpu = task_cpu(p);
tmn.to_cpu = new_cpu;
atomic_notifier_call_chain(&task_migration_notifier, 0, &tmn);
}
__set_task_cpu(p, new_cpu);