Commit-ID: 5b206d48e58204e84d249c4eb18651a1ff7a1274
Gitweb: http://git.kernel.org/tip/5b206d48e58204e84d249c4eb18651a1ff7a1274
Author: Frederic Weisbecker <fweisbec@xxxxxxxxx>
AuthorDate: Fri, 12 Jul 2013 19:05:14 +0200
Committer: Frederic Weisbecker <fweisbec@xxxxxxxxx>
CommitDate: Tue, 13 Aug 2013 00:40:44 +0200
vtime: Update a few comments
Update a stale comment from the old vtime era and document some
locking that might be non obvious.
Signed-off-by: Frederic Weisbecker <fweisbec@xxxxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Li Zhong <zhong@xxxxxxxxxxxxxxxxxx>
Cc: Mike Galbraith <efault@xxxxxx>
Cc: Kevin Hilman <khilman@xxxxxxxxxx>
---
include/linux/context_tracking.h | 10 ++++------
kernel/sched/cputime.c | 7 +++++++
2 files changed, 11 insertions(+), 6 deletions(-)
diff --git a/include/linux/context_tracking.h b/include/linux/context_tracking.h
index 5984f25..d883ff0 100644
--- a/include/linux/context_tracking.h
+++ b/include/linux/context_tracking.h
@@ -72,8 +72,9 @@ extern void guest_exit(void);
static inline void guest_enter(void)
{
/*
- * This is running in ioctl context so we can avoid
- * the call to vtime_account() with its unnecessary idle check.
+ * This is running in ioctl context so its safe
+ * to assume that it's the stime pending cputime
+ * to flush.
*/
vtime_account_system(current);
current->flags |= PF_VCPU;
@@ -81,10 +82,7 @@ static inline void guest_enter(void)
static inline void guest_exit(void)
{
- /*
- * This is running in ioctl context so we can avoid
- * the call to vtime_account() with its unnecessary idle check.
- */
+ /* Flush the guest cputime we spent on the guest */
vtime_account_system(current);
current->flags &= ~PF_VCPU;
}
diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c
index a7959e0..223a35e 100644
--- a/kernel/sched/cputime.c
+++ b/kernel/sched/cputime.c
@@ -712,6 +712,13 @@ void vtime_user_enter(struct task_struct *tsk)
void vtime_guest_enter(struct task_struct *tsk)
{
+ /*
+ * The flags must be updated under the lock with
+ * the vtime_snap flush and update.
+ * That enforces a right ordering and update sequence
+ * synchronization against the reader (task_gtime())
+ * that can thus safely catch up with a tickless delta.
+ */
write_seqlock(&tsk->vtime_seqlock);
__vtime_account_system(tsk);
current->flags |= PF_VCPU;
--
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