On Wed, 2013-07-17 at 18:44 +0200, Frederic Weisbecker wrote:
> Update a stale comment from the old vtime era and document some
> locking that might be non obvious.
>
> Signed-off-by: Frederic Weisbecker <fweis...@gmail.com>
> Cc: Steven Rostedt <rost...@goodmis.org>
> Cc: Paul E. McKenney <paul...@linux.vnet.ibm.com>
> Cc: Ingo Molnar <mi...@kernel.org>
> Cc: Thomas Gleixner <t...@linutronix.de>
> Cc: Peter Zijlstra <pet...@infradead.org>
> Cc: Borislav Petkov <b...@alien8.de>
> Cc: Li Zhong <zh...@linux.vnet.ibm.com>
> Cc: Mike Galbraith <efa...@gmx.de>
> Cc: Kevin Hilman <khil...@linaro.org>
> ---
> include/linux/context_tracking.h | 8 ++------
> kernel/sched/cputime.c | 7 +++++++
> 2 files changed, 9 insertions(+), 6 deletions(-)
>
> diff --git a/include/linux/context_tracking.h
> b/include/linux/context_tracking.h
> index 5984f25..12045ce 100644
> --- a/include/linux/context_tracking.h
> +++ b/include/linux/context_tracking.h
> @@ -72,8 +72,8 @@ 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 the pending cputime to flush is stime.
The above is worded funny. What about:
"This is running in ioctl context so its safe to assume that its the
stime pending cputime to flush"
I don't know. But "is stime" is what made me have to read that three
times to figure out what you meant.
> */
> vtime_account_system(current);
> current->flags |= PF_VCPU;
> @@ -81,10 +81,6 @@ 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.
> - */
Should we copy the comment here too?
-- Steve
> 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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