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    Subject[PATCH 7/8] ACPI: acpi_idle: touch TS_POLLING only in the non-MWAIT case
    Date
    From: Len Brown <len.brown@intel.com>

    commit d306ebc28649b89877a22158fe0076f06cc46f60
    (ACPI: Be in TS_POLLING state during mwait based C-state entry)
    fixed an important power & performance issue where ACPI c2 and c3 C-states
    were clearing TS_POLLING even when using MWAIT (ACPI_STATE_FFH).
    That bug had been causing us to receive redundant scheduling interrups
    when we had already been woken up by MONITOR/MWAIT.

    Following up on that...

    In the MWAIT case, we don't have to subsequently
    check need_resched(), as that c heck was there
    for the TS_POLLING-clearing case.

    Note that not only does the cpuidle calling function
    already check need_resched() before calling us, the
    low-level entry into monitor/mwait calls it twice --
    guaranteeing that a write to the trigger address
    can not go un-noticed.

    Also, in this case, we don't have to set TS_POLLING
    when we wake, because we never cleared it.

    Signed-off-by: Len Brown <len.brown@intel.com>
    Cc: Venkatesh Pallipadi <venki@google.com>
    ---
    drivers/acpi/processor_idle.c | 28 ++++++++++++++++------------
    1 files changed, 16 insertions(+), 12 deletions(-)

    diff --git a/drivers/acpi/processor_idle.c b/drivers/acpi/processor_idle.c
    index 5939e7f..a4166e2 100644
    --- a/drivers/acpi/processor_idle.c
    +++ b/drivers/acpi/processor_idle.c
    @@ -881,6 +881,7 @@ static int acpi_idle_enter_simple(struct cpuidle_device *dev,
    return(acpi_idle_enter_c1(dev, state));

    local_irq_disable();
    +
    if (cx->entry_method != ACPI_CSTATE_FFH) {
    current_thread_info()->status &= ~TS_POLLING;
    /*
    @@ -888,12 +889,12 @@ static int acpi_idle_enter_simple(struct cpuidle_device *dev,
    * NEED_RESCHED:
    */
    smp_mb();
    - }

    - if (unlikely(need_resched())) {
    - current_thread_info()->status |= TS_POLLING;
    - local_irq_enable();
    - return 0;
    + if (unlikely(need_resched())) {
    + current_thread_info()->status |= TS_POLLING;
    + local_irq_enable();
    + return 0;
    + }
    }

    /*
    @@ -918,7 +919,8 @@ static int acpi_idle_enter_simple(struct cpuidle_device *dev,
    sched_clock_idle_wakeup_event(sleep_ticks*PM_TIMER_TICK_NS);

    local_irq_enable();
    - current_thread_info()->status |= TS_POLLING;
    + if (cx->entry_method != ACPI_CSTATE_FFH)
    + current_thread_info()->status |= TS_POLLING;

    cx->usage++;

    @@ -968,6 +970,7 @@ static int acpi_idle_enter_bm(struct cpuidle_device *dev,
    }

    local_irq_disable();
    +
    if (cx->entry_method != ACPI_CSTATE_FFH) {
    current_thread_info()->status &= ~TS_POLLING;
    /*
    @@ -975,12 +978,12 @@ static int acpi_idle_enter_bm(struct cpuidle_device *dev,
    * NEED_RESCHED:
    */
    smp_mb();
    - }

    - if (unlikely(need_resched())) {
    - current_thread_info()->status |= TS_POLLING;
    - local_irq_enable();
    - return 0;
    + if (unlikely(need_resched())) {
    + current_thread_info()->status |= TS_POLLING;
    + local_irq_enable();
    + return 0;
    + }
    }

    acpi_unlazy_tlb(smp_processor_id());
    @@ -1032,7 +1035,8 @@ static int acpi_idle_enter_bm(struct cpuidle_device *dev,
    sched_clock_idle_wakeup_event(sleep_ticks*PM_TIMER_TICK_NS);

    local_irq_enable();
    - current_thread_info()->status |= TS_POLLING;
    + if (cx->entry_method != ACPI_CSTATE_FFH)
    + current_thread_info()->status |= TS_POLLING;

    cx->usage++;

    --
    1.6.0.6


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