From: Frederic Weisbecker Date: Wed, 6 Nov 2013 14:42:04 +0000 (+0100) Subject: posix-timers: Spare workqueue if there is no full dynticks CPU to kick X-Git-Url: https://git.stricted.de/?a=commitdiff_plain;h=d4283c654130c3d01b6842d3821dbdc3c15ceb46;p=GitHub%2FLineageOS%2FG12%2Fandroid_kernel_amlogic_linux-4.9.git posix-timers: Spare workqueue if there is no full dynticks CPU to kick After a posix cpu timer is set, a workqueue is scheduled in order to kick the full dynticks CPUs and let them restart their tick if necessary in case the task they are running is concerned by the new timer. This kick is implemented by way of IPIs, which require interrupts to be enabled, hence the need for a workqueue to raise them because the posix cpu timer set path has interrupts disabled. Now if there is no full dynticks CPU on the system, the workqueue is still scheduled but it simply won't send any IPI and return immediately. So lets spare that worqueue when it is not needed. Signed-off-by: Frederic Weisbecker Cc: Thomas Gleixner Cc: Ingo Molnar Cc: Peter Zijlstra Cc: Oleg Nesterov Cc: Steven Rostedt --- diff --git a/kernel/posix-cpu-timers.c b/kernel/posix-cpu-timers.c index c7f31aa272f7..35509c5a3ffb 100644 --- a/kernel/posix-cpu-timers.c +++ b/kernel/posix-cpu-timers.c @@ -608,7 +608,8 @@ static DECLARE_WORK(nohz_kick_work, nohz_kick_work_fn); */ static void posix_cpu_timer_kick_nohz(void) { - schedule_work(&nohz_kick_work); + if (context_tracking_is_enabled()) + schedule_work(&nohz_kick_work); } bool posix_cpu_timers_can_stop_tick(struct task_struct *tsk)