• Peter Zijlstra's avatar
    sched/idle: Add support for tasks that inject idle · c1de45ca
    Peter Zijlstra authored
    
    
    Idle injection drivers such as Intel powerclamp and ACPI PAD drivers use
    realtime tasks to take control of CPU then inject idle. There are two
    issues with this approach:
    
     1. Low efficiency: injected idle task is treated as busy so sched ticks
        do not stop during injected idle period, the result of these
        unwanted wakeups can be ~20% loss in power savings.
    
     2. Idle accounting: injected idle time is presented to user as busy.
    
    This patch addresses the issues by introducing a new PF_IDLE flag which
    allows any given task to be treated as idle task while the flag is set.
    Therefore, idle injection tasks can run through the normal flow of NOHZ
    idle enter/exit to get the correct accounting as well as tick stop when
    possible.
    
    The implication is that idle task is then no longer limited to PID == 0.
    Acked-by: default avatarIngo Molnar <mingo@kernel.org>
    Signed-off-by: default avatarPeter Zijlstra <peterz@infradead.org>
    Signed-off-by: default avatarJacob Pan <jacob.jun.pan@linux.intel.com>
    Signed-off-by: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
    c1de45ca