linux-kernel - [PATCH] posix-cpu-timers: reset expire cache when no timer is running

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Message-ID: <20091117125702.GA3658@dhcp-lab-161.englab.brq.redhat.com>
Date:	Tue, 17 Nov 2009 13:57:03 +0100
From:	Stanislaw Gruszka <sgruszka@...hat.com>
To:	Ingo Molnar <mingo@...e.hu>, Oleg Nesterov <oleg@...hat.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>,
	Spencer Candland <spencer@...ehost.com>,
	linux-kernel@...r.kernel.org
Subject: [PATCH] posix-cpu-timers: reset expire cache when no timer is
	running

When process delete cpu timer or timer expires we do not clear
expiration cache sig->cputimer_expires. This create situation when in
fastpath_timer_check() we _on_ cputimer (together with loop on all
threads) just to turn in off in check_process_timers(). We not
necessary go to slowpath and not necessary loop on all threads in
fastpath - and this is repeated on every tick.

To fix we zero sig->cputimer_expires in stop_process_timers().

Signed-off-by: Stanislaw Gruszka <sgruszka@...hat.com>
---
 kernel/posix-cpu-timers.c |   10 +++++++---
 1 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/kernel/posix-cpu-timers.c b/kernel/posix-cpu-timers.c
index 5c9dc22..ac54986 100644
--- a/kernel/posix-cpu-timers.c
+++ b/kernel/posix-cpu-timers.c
@@ -1061,9 +1061,9 @@ static void check_thread_timers(struct task_struct *tsk,
 	}
 }
 
-static void stop_process_timers(struct task_struct *tsk)
+static void stop_process_timers(struct signal_struct *sig)
 {
-	struct thread_group_cputimer *cputimer = &tsk->signal->cputimer;
+	struct thread_group_cputimer *cputimer = &sig->cputimer;
 	unsigned long flags;
 
 	if (!cputimer->running)
@@ -1072,6 +1072,10 @@ static void stop_process_timers(struct task_struct *tsk)
 	spin_lock_irqsave(&cputimer->lock, flags);
 	cputimer->running = 0;
 	spin_unlock_irqrestore(&cputimer->lock, flags);
+
+	sig->cputime_expires.prof_exp = cputime_zero;
+	sig->cputime_expires.virt_exp = cputime_zero;
+	sig->cputime_expires.sched_exp = 0;
 }
 
 static u32 onecputick;
@@ -1132,7 +1136,7 @@ static void check_process_timers(struct task_struct *tsk,
 	    list_empty(&timers[CPUCLOCK_VIRT]) &&
 	    cputime_eq(sig->it[CPUCLOCK_VIRT].expires, cputime_zero) &&
 	    list_empty(&timers[CPUCLOCK_SCHED])) {
-		stop_process_timers(tsk);
+		stop_process_timers(sig);
 		return;
 	}
 
-- 
1.6.2.5

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