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authorIngo Molnar <mingo@elte.hu>2009-05-07 11:18:34 +0200
committerIngo Molnar <mingo@elte.hu>2009-05-07 13:36:22 +0200
commit0ad5d703c6c0fcd385d956555460df95dff7eb7e (patch)
tree4b777100f9be4fe90ca4bd043b9f98df672b5b3b /kernel/sched.c
parent44347d947f628060b92449702071bfe1d31dfb75 (diff)
parent1cb81b143fa8f0e4629f10690862e2e52ca792ff (diff)
Merge branch 'tracing/hw-branch-tracing' into tracing/core
Merge reason: this topic is ready for upstream now. It passed Oleg's review and Andrew had no further mm/* objections/observations either. Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'kernel/sched.c')
-rw-r--r--kernel/sched.c43
1 files changed, 43 insertions, 0 deletions
diff --git a/kernel/sched.c b/kernel/sched.c
index 14a19b17674..6530a27052f 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -2011,6 +2011,49 @@ migrate_task(struct task_struct *p, int dest_cpu, struct migration_req *req)
}
/*
+ * wait_task_context_switch - wait for a thread to complete at least one
+ * context switch.
+ *
+ * @p must not be current.
+ */
+void wait_task_context_switch(struct task_struct *p)
+{
+ unsigned long nvcsw, nivcsw, flags;
+ int running;
+ struct rq *rq;
+
+ nvcsw = p->nvcsw;
+ nivcsw = p->nivcsw;
+ for (;;) {
+ /*
+ * The runqueue is assigned before the actual context
+ * switch. We need to take the runqueue lock.
+ *
+ * We could check initially without the lock but it is
+ * very likely that we need to take the lock in every
+ * iteration.
+ */
+ rq = task_rq_lock(p, &flags);
+ running = task_running(rq, p);
+ task_rq_unlock(rq, &flags);
+
+ if (likely(!running))
+ break;
+ /*
+ * The switch count is incremented before the actual
+ * context switch. We thus wait for two switches to be
+ * sure at least one completed.
+ */
+ if ((p->nvcsw - nvcsw) > 1)
+ break;
+ if ((p->nivcsw - nivcsw) > 1)
+ break;
+
+ cpu_relax();
+ }
+}
+
+/*
* wait_task_inactive - wait for a thread to unschedule.
*
* If @match_state is nonzero, it's the @p->state value just checked and