Commit 934715a1 authored Oct 14, 2015 by Jason Low Committed by Thomas Gleixner Oct 15, 2015

posix_cpu_timer: Check thread timers only when there are active thread timers



The fastpath_timer_check() contains logic to check for if any timers
are set by checking if !task_cputime_zero(). Similarly, we can do this
before calling check_thread_timers(). In the case where there
are only process-wide timers, this will skip all of the computations for
per-thread timers when there are no per-thread timers.

As suggested by George, we can put the task_cputime_zero() check in
check_thread_timers(), since that is more of an optization to the
function. Similarly, we move the existing check of cputimer->running
to check_process_timers().

Signed-off-by: Jason Low <jason.low2@hp.com>
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Reviewed-by: George Spelvin <linux@horizon.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: hideaki.kimura@hpe.com
Cc: terry.rudd@hpe.com
Cc: scott.norton@hpe.com
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1444849677-29330-3-git-send-email-jason.low2@hp.com


Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

parent 7c177d99

kernel/time/posix-cpu-timers.c

+16 −6

Original line number	Diff line number	Diff line
		@@ -864,6 +864,13 @@ static void check_thread_timers(struct task_struct *tsk,
		unsigned long long expires;
		unsigned long soft;

		/*
		* If cputime_expires is zero, then there are no active
		* per thread CPU timers.
		*/
		if (task_cputime_zero(&tsk->cputime_expires))
		return;

		expires = check_timers_list(timers, firing, prof_ticks(tsk));
		tsk_expires->prof_exp = expires_to_cputime(expires);

		@@ -961,6 +968,13 @@ static void check_process_timers(struct task_struct *tsk,
		struct task_cputime cputime;
		unsigned long soft;

		/*
		* If cputimer is not running, then there are no active
		* process wide timers (POSIX 1.b, itimers, RLIMIT_CPU).
		*/
		if (!READ_ONCE(tsk->signal->cputimer.running))
		return;

		/*
		* Collect the current process totals.
		*/
		@@ -1169,11 +1183,7 @@ void run_posix_cpu_timers(struct task_struct *tsk)
		* put them on the firing list.
		*/
		check_thread_timers(tsk, &firing);
		/*
		* If there are any active process wide timers (POSIX 1.b, itimers,
		* RLIMIT_CPU) cputimer must be running.
		*/
		if (READ_ONCE(tsk->signal->cputimer.running))

		check_process_timers(tsk, &firing);

		/*