linux-kernel - [PATCH 2/3] timer: Check thread timers only when there are active thread timers

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Date:	Tue, 25 Aug 2015 20:17:47 -0700
From:	Jason Low <jason.low2@...com>
To:	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Oleg Nesterov <oleg@...hat.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	linux-kernel@...r.kernel.org,
	Frederic Weisbecker <fweisbec@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Davidlohr Bueso <dave@...olabs.net>,
	Steven Rostedt <rostedt@...dmis.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Terry Rudd <terry.rudd@...com>, Rik van Riel <riel@...hat.com>,
	Scott J Norton <scott.norton@...com>,
	Jason Low <jason.low2@...com>
Subject: [PATCH 2/3] 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 the computations for
the per-thread timers when there are no per-thread timers.

Signed-off-by: Jason Low <jason.low2@...com>
---
 kernel/time/posix-cpu-timers.c |   10 ++++++----
 1 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/kernel/time/posix-cpu-timers.c b/kernel/time/posix-cpu-timers.c
index 02596ff..535bef5 100644
--- a/kernel/time/posix-cpu-timers.c
+++ b/kernel/time/posix-cpu-timers.c
@@ -1168,11 +1168,13 @@ void run_posix_cpu_timers(struct task_struct *tsk)
 	if (!lock_task_sighand(tsk, &flags))
 		return;
 	/*
-	 * Here we take off tsk->signal->cpu_timers[N] and
-	 * tsk->cpu_timers[N] all the timers that are firing, and
-	 * put them on the firing list.
+	 * If there are active per-thread timers, take off
+	 * tsk->signal->cpu_timers[N] and tsk->cpu_timers[N] all the
+	 * timers that are firing, and put them on the firing list.
 	 */
-	check_thread_timers(tsk, &firing);
+	if (!task_cputime_zero(&tsk->cputime_expires))
+		check_thread_timers(tsk, &firing);
+
 	/*
 	 * If there are any active process wide timers (POSIX 1.b, itimers,
 	 * RLIMIT_CPU) cputimer must be running.
-- 
1.7.2.5

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