Add a notifier to publish when a task gets migrated from one cpu to
another. The first intended use is to export a "migration counter"
to usermode so that a task can tell whether its still running on the
same cpu (for use in vgetcpu and other vsyscall code).
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@xxxxxxxxxx>
Cc: Avi Kivity <avi@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxx>
Cc: Andi Kleen <ak@xxxxxxxxxxxxxxx>
---
include/linux/sched.h | 8 ++++++++
kernel/sched.c | 14 ++++++++++++++
2 files changed, 22 insertions(+), 0 deletions(-)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 0f1ea4a..5186dd9 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -141,6 +141,14 @@ extern unsigned long nr_iowait(void);
extern void calc_global_load(void);
extern u64 cpu_nr_migrations(int cpu);
+/* Notifier for when a task gets migrated to a new CPU */
+struct task_migration_notifier {
+ struct task_struct *task;
+ int from_cpu;
+ int to_cpu;
+};
+extern void register_task_migration_notifier(struct notifier_block *n);
+
extern unsigned long get_parent_ip(unsigned long addr);
struct seq_file;
diff --git a/kernel/sched.c b/kernel/sched.c
index 1b59e26..3982e8e 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -1951,6 +1951,12 @@ task_hot(struct task_struct *p, u64 now, struct
sched_domain *sd)
return delta < (s64)sysctl_sched_migration_cost;
}
+static ATOMIC_NOTIFIER_HEAD(task_migration_notifier);
+
+void register_task_migration_notifier(struct notifier_block *n)
+{
+ atomic_notifier_chain_register(&task_migration_notifier, n);
+}
void set_task_cpu(struct task_struct *p, unsigned int new_cpu)
{
@@ -1973,6 +1979,8 @@ void set_task_cpu(struct task_struct *p, unsigned int
new_cpu)
p->se.block_start -= clock_offset;
#endif
if (old_cpu != new_cpu) {
+ struct task_migration_notifier tmn;
+
p->se.nr_migrations++;
new_rq->nr_migrations_in++;
#ifdef CONFIG_SCHEDSTATS
@@ -1981,6 +1989,12 @@ void set_task_cpu(struct task_struct *p, unsigned int
new_cpu)
#endif
perf_swcounter_event(PERF_COUNT_SW_CPU_MIGRATIONS,
1, 1, NULL, 0);
+
+ tmn.task = p;
+ tmn.from_cpu = old_cpu;
+ tmn.to_cpu = new_cpu;
+
+ atomic_notifier_call_chain(&task_migration_notifier, 0, &tmn);
}
p->se.vruntime -= old_cfsrq->min_vruntime -
new_cfsrq->min_vruntime;
--
1.6.2.5
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