• Daniel Lezcano's avatar
    cpuidle: Fix cpuidle_state_is_coupled() argument in cpuidle_enter() · e7387da5
    Daniel Lezcano authored
    Commit 0b89e9aa (cpuidle: delay enabling interrupts until all
    coupled CPUs leave idle) rightfully fixed a regression by letting
    the coupled idle state framework to handle local interrupt enabling
    when the CPU is exiting an idle state.
    
    The current code checks if the idle state is coupled and, if so, it
    will let the coupled code to enable interrupts. This way, it can
    decrement the ready-count before handling the interrupt. This
    mechanism prevents the other CPUs from waiting for a CPU which is
    handling interrupts.
    
    But the check is done against the state index returned by the back
    end driver's ->enter functions which could be different from the
    initial index passed as parameter to the cpuidle_enter_state()
    function.
    
     entered_state = target_state->enter(dev, drv, index);
    
     [ ... ]
    
     if (!cpuidle_state_is_coupled(drv, entered_state))
    	local_irq_enable();
    
     [ ... ]
    
    If the 'index' is referring to a coupled idle state but the
    'entered_state' is *not* coupled, then the interrupts are enabled
    again. All CPUs blocked on the sync barrier may busy loop longer
    if the CPU has interrupts to handle before decrementing the
    ready-count. That's consuming more energy than saving.
    
    Fixes: 0b89e9aa
    
     (cpuidle: delay enabling interrupts until all coupled CPUs leave idle)
    Signed-off-by: default avatarDaniel Lezcano <daniel.lezcano@linaro.org>
    Cc: 3.15+ <stable@vger.kernel.org> # 3.15+
    [ rjw: Subject & changelog ]
    Signed-off-by: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
    e7387da5