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| author | Frederic Weisbecker <fweisbec@gmail.com> | 2013-07-12 21:05:14 +0400 |
|---|---|---|
| committer | Frederic Weisbecker <fweisbec@gmail.com> | 2013-08-13 02:40:44 +0400 |
| commit | 5b206d48e58204e84d249c4eb18651a1ff7a1274 (patch) | |
| tree | c97a8158df0ff854d1d6389ddde5cc1fa53bae92 | |
| parent | 2d854e5738cded368a0759f85b1197f5c044513d (diff) | |
| download | linux-5b206d48e58204e84d249c4eb18651a1ff7a1274.tar.xz | |
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@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Li Zhong <zhong@linux.vnet.ibm.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Kevin Hilman <khilman@linaro.org>
| -rw-r--r-- | include/linux/context_tracking.h | 10 | ||||
| -rw-r--r-- | 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 5984f2556d13..d883ff0dd8fc 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 a7959e05a9d5..223a35efa0a6 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; |