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    Subject[PATCH 3/4] sched: Pull preemption disablement to __schedule() caller
    Date
    Lets factorize all preempt_count operations to the __schedule()
    callers. This way we spare two preempt count changes in __schedule()
    when it's called by preemption APIs.

    Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Steven Rostedt <rostedt@goodmis.org>
    Cc: Ingo Molnar <mingo@kernel.org>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
    ---
    kernel/sched/core.c | 18 ++++++++----------
    1 file changed, 8 insertions(+), 10 deletions(-)

    diff --git a/kernel/sched/core.c b/kernel/sched/core.c
    index 89b165f..1c0e5b1 100644
    --- a/kernel/sched/core.c
    +++ b/kernel/sched/core.c
    @@ -2760,7 +2760,6 @@ static void __sched __schedule(void)
    struct rq *rq;
    int cpu;

    - preempt_disable();
    cpu = smp_processor_id();
    rq = cpu_rq(cpu);
    rcu_note_context_switch();
    @@ -2822,8 +2821,6 @@ static void __sched __schedule(void)
    raw_spin_unlock_irq(&rq->lock);

    post_schedule(rq);
    -
    - sched_preempt_enable_no_resched();
    }

    static inline void sched_submit_work(struct task_struct *tsk)
    @@ -2844,7 +2841,9 @@ asmlinkage __visible void __sched schedule(void)

    sched_submit_work(tsk);
    do {
    + preempt_disable();
    __schedule();
    + sched_preempt_enable_no_resched();
    } while (need_resched());
    }
    EXPORT_SYMBOL(schedule);
    @@ -2883,9 +2882,9 @@ void __sched schedule_preempt_disabled(void)
    static void preempt_schedule_common(void)
    {
    do {
    - preempt_count_add(PREEMPT_ACTIVE);
    + preempt_count_add(PREEMPT_ACTIVE + PREEMPT_CHECK_OFFSET);
    __schedule();
    - preempt_count_sub(PREEMPT_ACTIVE);
    + preempt_count_sub(PREEMPT_ACTIVE + PREEMPT_CHECK_OFFSET);

    /*
    * Check again in case we missed a preemption opportunity
    @@ -2938,7 +2937,7 @@ asmlinkage __visible void __sched notrace preempt_schedule_context(void)
    return;

    do {
    - preempt_count_add(PREEMPT_ACTIVE);
    + preempt_count_add(PREEMPT_ACTIVE + PREEMPT_CHECK_OFFSET);
    /*
    * Needs preempt disabled in case user_exit() is traced
    * and the tracer calls preempt_enable_notrace() causing
    @@ -2947,8 +2946,7 @@ asmlinkage __visible void __sched notrace preempt_schedule_context(void)
    prev_ctx = exception_enter();
    __schedule();
    exception_exit(prev_ctx);
    -
    - preempt_count_sub(PREEMPT_ACTIVE);
    + preempt_count_sub(PREEMPT_ACTIVE + PREEMPT_CHECK_OFFSET);
    barrier();
    } while (need_resched());
    }
    @@ -2973,11 +2971,11 @@ asmlinkage __visible void __sched preempt_schedule_irq(void)
    prev_state = exception_enter();

    do {
    - preempt_count_add(PREEMPT_ACTIVE);
    + preempt_count_add(PREEMPT_ACTIVE + PREEMPT_CHECK_OFFSET);
    local_irq_enable();
    __schedule();
    local_irq_disable();
    - preempt_count_sub(PREEMPT_ACTIVE);
    + preempt_count_sub(PREEMPT_ACTIVE + PREEMPT_CHECK_OFFSET);

    /*
    * Check again in case we missed a preemption opportunity
    --
    2.1.4


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