• Rafael J. Wysocki's avatar
    cpuidle: menu: Handle stopped tick more aggressively · 5ef499cd
    Rafael J. Wysocki authored
    Commit 87c9fe6e (cpuidle: menu: Avoid selecting shallow states
    with stopped tick) missed the case when the target residencies of
    deep idle states of CPUs are above the tick boundary which may cause
    the CPU to get stuck in a shallow idle state for a long time.
    
    Say there are two CPU idle states available: one shallow, with the
    target residency much below the tick boundary and one deep, with
    the target residency significantly above the tick boundary.  In
    that case, if the tick has been stopped already and the expected
    next timer event is relatively far in the future, the governor will
    assume the idle duration to be equal to TICK_USEC and it will select
    the idle state for the CPU accordingly.  However, that will cause the
    shallow state to be selected even though it would have been more
    energy-efficient to select the deep one.
    
    To address this issue, modify the governor to always use the time
    till the closest timer event instead of the predicted idle duration
    if the latter is less than the tick period length and the tick has
    been stopped already.  Also make it extend the search for a matching
    idle state if the tick is stopped to avoid settling on a shallow
    state if deep states with target residencies above the tick period
    length are available.
    
    In addition, make it always indicate that the tick should be stopped
    if it has been stopped already for consistency.
    
    Fixes: 87c9fe6e (cpuidle: menu: Avoid selecting shallow states with stopped tick)
    Reported-by: default avatarLeo Yan <leo.yan@linaro.org>
    Acked-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
    Cc: 4.17+ <stable@vger.kernel.org> # 4.17+
    Signed-off-by: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
    5ef499cd
menu.c 18 KB