posix-timers: Spare workqueue if there is no full dynticks CPU to kick
authorFrederic Weisbecker <fweisbec@gmail.com>
Wed, 6 Nov 2013 14:42:04 +0000 (15:42 +0100)
committerFrederic Weisbecker <fweisbec@gmail.com>
Mon, 2 Dec 2013 19:43:16 +0000 (20:43 +0100)
commitd4283c654130c3d01b6842d3821dbdc3c15ceb46
tree2fa770f2500b88bb42ebcb2bfcde4a738049638f
parentd0df09ebfc126b23c1005f98ddecc9907f9c5d25
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 <fweisbec@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
kernel/posix-cpu-timers.c