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vtime: Update a few comments

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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>
This commit is contained in:
Frederic Weisbecker 2013-07-12 19:05:14 +02:00
parent 2d854e5738
commit 5b206d48e5
2 changed files with 11 additions and 6 deletions
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10
include/linux/context_tracking.h
View File

@ -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;
}

7
kernel/sched/cputime.c
View File

@ -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;