diff options
| author | Peter Zijlstra <peterz@infradead.org> | 2015-09-28 17:52:18 +0200 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2015-10-06 17:08:14 +0200 |
| commit | 609ca066386b2e64d4c0b0f55da327654962a0c9 (patch) | |
| tree | 11b4faacc00bbc39d967374df633f6c352ce199b /include/linux/sched.h | |
| parent | b99def8b961448f5b9a550dddeeb718e3975e7a6 (diff) | |
sched/core: Create preempt_count invariant
Assuming units of PREEMPT_DISABLE_OFFSET for preempt_count() numbers.
Now that TASK_DEAD no longer results in preempt_count() == 3 during
scheduling, we will always call context_switch() with preempt_count()
== 2.
However, we don't always end up with preempt_count() == 2 in
finish_task_switch() because new tasks get created with
preempt_count() == 1.
Create FORK_PREEMPT_COUNT and set it to 2 and use that in the right
places. Note that we cannot use INIT_PREEMPT_COUNT as that serves
another purpose (boot).
After this, preempt_count() is invariant across the context switch,
with exception of PREEMPT_ACTIVE.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'include/linux/sched.h')
| -rw-r--r-- | include/linux/sched.h | 17 |
1 files changed, 12 insertions, 5 deletions
diff --git a/include/linux/sched.h b/include/linux/sched.h index e5b8cbc4b8d6..23ca455d9582 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -599,11 +599,7 @@ struct task_cputime_atomic { .sum_exec_runtime = ATOMIC64_INIT(0), \ } -#ifdef CONFIG_PREEMPT_COUNT -#define PREEMPT_DISABLED (1 + PREEMPT_ENABLED) -#else -#define PREEMPT_DISABLED PREEMPT_ENABLED -#endif +#define PREEMPT_DISABLED (PREEMPT_DISABLE_OFFSET + PREEMPT_ENABLED) /* * Disable preemption until the scheduler is running -- use an unconditional @@ -613,6 +609,17 @@ struct task_cputime_atomic { */ #define INIT_PREEMPT_COUNT PREEMPT_OFFSET +/* + * Initial preempt_count value; reflects the preempt_count schedule invariant + * which states that during context switches: + * + * preempt_count() == 2*PREEMPT_DISABLE_OFFSET + * + * Note: PREEMPT_DISABLE_OFFSET is 0 for !PREEMPT_COUNT kernels. + * Note: See finish_task_switch(). + */ +#define FORK_PREEMPT_COUNT (2*PREEMPT_DISABLE_OFFSET + PREEMPT_ENABLED) + /** * struct thread_group_cputimer - thread group interval timer counts * @cputime_atomic: atomic thread group interval timers. |