Commit-ID: a26b89f05d194413c7238e0bea071054f6b5d3c8
Gitweb: http://git.kernel.org/tip/a26b89f05d194413c7238e0bea071054f6b5d3c8
Author: Markus Metzger <markus.t.metzger@xxxxxxxxx>
AuthorDate: Fri, 3 Apr 2009 16:43:34 +0200
Committer: Ingo Molnar <mingo@xxxxxxx>
CommitDate: Tue, 7 Apr 2009 13:36:12 +0200
sched, hw-branch-tracer: add wait_task_context_switch() function to sched.h
Add a function to wait until some other task has been
switched out at least once.
This differs from wait_task_inactive() subtly, in that the
latter will wait until the task has left the CPU.
Signed-off-by: Markus Metzger <markus.t.metzger@xxxxxxxxx>
Cc: markus.t.metzger@xxxxxxxxx
Cc: roland@xxxxxxxxxx
Cc: eranian@xxxxxxxxxxxxxx
Cc: oleg@xxxxxxxxxx
Cc: juan.villacis@xxxxxxxxx
Cc: ak@xxxxxxxxxxxxxxxxxx
LKML-Reference: <20090403144549.794157000@xxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxx>
---
include/linux/sched.h | 2 ++
kernel/sched.c | 43 +++++++++++++++++++++++++++++++++++++++++++
2 files changed, 45 insertions(+), 0 deletions(-)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index b94f354..a5b9a83 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1993,8 +1993,10 @@ extern void set_task_comm(struct task_struct *tsk, char *from);
extern char *get_task_comm(char *to, struct task_struct *tsk);
#ifdef CONFIG_SMP
+extern void wait_task_context_switch(struct task_struct *p);
extern unsigned long wait_task_inactive(struct task_struct *, long match_state);
#else
+static inline void wait_task_context_switch(struct task_struct *p) {}
static inline unsigned long wait_task_inactive(struct task_struct *p,
long match_state)
{
diff --git a/kernel/sched.c b/kernel/sched.c
index 6cc1fd5..f91bc81 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -2003,6 +2003,49 @@ 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
--
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