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Commit 29f87b79 authored by Stanislaw Gruszka's avatar Stanislaw Gruszka Committed by Thomas Gleixner
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posix-cpu-timers: Optimize run_posix_cpu_timers() 



We can optimize and simplify things taking into account signal->cputimer
is always running when we have configured any process wide cpu timer.

In check_process_timers(), we don't have to check if new updated value of
signal->cputime_expires is smaller, since we maintain new first expiration
time ({prof,virt,sched}_expires) in code flow and all other writes to
expiration cache are protected by sighand->siglock .

Signed-off-by: default avatarStanislaw Gruszka <sgruszka@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
parent dbb6be6d

kernel/posix-cpu-timers.c

+29 −51
Original line number Diff line number Diff line
@@ -1002,16 +1002,9 @@ static void stop_process_timers(struct signal_struct *sig) 
	struct thread_group_cputimer *cputimer = &sig->cputimer;

	unsigned long flags;



	if (!cputimer->running)

		return;



	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;
@@ -1048,6 +1041,23 @@ static void check_cpu_itimer(struct task_struct *tsk, struct cpu_itimer *it, 
	}

}



/**

 * task_cputime_zero - Check a task_cputime struct for all zero fields.

 *

 * @cputime:	The struct to compare.

 *

 * Checks @cputime to see if all fields are zero.  Returns true if all fields

 * are zero, false if any field is nonzero.

 */

static inline int task_cputime_zero(const struct task_cputime *cputime)

{

	if (cputime_eq(cputime->utime, cputime_zero) &&

	    cputime_eq(cputime->stime, cputime_zero) &&

	    cputime->sum_exec_runtime == 0)

		return 1;

	return 0;

}



/*

 * Check for any per-thread CPU timers that have fired and move them

 * off the tsk->*_timers list onto the firing list.  Per-thread timers
@@ -1064,19 +1074,6 @@ static void check_process_timers(struct task_struct *tsk, 
	struct task_cputime cputime;

	unsigned long soft;



	/*

	 * Don't sample the current process CPU clocks if there are no timers.

	 */

	if (list_empty(&timers[CPUCLOCK_PROF]) &&

	    cputime_eq(sig->it[CPUCLOCK_PROF].expires, cputime_zero) &&

	    sig->rlim[RLIMIT_CPU].rlim_cur == RLIM_INFINITY &&

	    list_empty(&timers[CPUCLOCK_VIRT]) &&

	    cputime_eq(sig->it[CPUCLOCK_VIRT].expires, cputime_zero) &&

	    list_empty(&timers[CPUCLOCK_SCHED])) {

		stop_process_timers(sig);

		return;

	}



	/*

	 * Collect the current process totals.

	 */
@@ -1166,18 +1163,11 @@ static void check_process_timers(struct task_struct *tsk, 
		}

	}



	if (!cputime_eq(prof_expires, cputime_zero) &&

	    (cputime_eq(sig->cputime_expires.prof_exp, cputime_zero) ||

	     cputime_gt(sig->cputime_expires.prof_exp, prof_expires)))

	sig->cputime_expires.prof_exp = prof_expires;

	if (!cputime_eq(virt_expires, cputime_zero) &&

	    (cputime_eq(sig->cputime_expires.virt_exp, cputime_zero) ||

	     cputime_gt(sig->cputime_expires.virt_exp, virt_expires)))

	sig->cputime_expires.virt_exp = virt_expires;

	if (sched_expires != 0 &&

	    (sig->cputime_expires.sched_exp == 0 ||

	     sig->cputime_expires.sched_exp > sched_expires))

	sig->cputime_expires.sched_exp = sched_expires;

	if (task_cputime_zero(&sig->cputime_expires))

		stop_process_timers(sig);

}



/*
@@ -1249,23 +1239,6 @@ out: 
	++timer->it_requeue_pending;

}



/**

 * task_cputime_zero - Check a task_cputime struct for all zero fields.

 *

 * @cputime:	The struct to compare.

 *

 * Checks @cputime to see if all fields are zero.  Returns true if all fields

 * are zero, false if any field is nonzero.

 */

static inline int task_cputime_zero(const struct task_cputime *cputime)

{

	if (cputime_eq(cputime->utime, cputime_zero) &&

	    cputime_eq(cputime->stime, cputime_zero) &&

	    cputime->sum_exec_runtime == 0)

		return 1;

	return 0;

}



/**

 * task_cputime_expired - Compare two task_cputime entities.

 *
@@ -1322,7 +1295,7 @@ static inline int fastpath_timer_check(struct task_struct *tsk) 
	}



	sig = tsk->signal;

	if (!task_cputime_zero(&sig->cputime_expires)) {

	if (sig->cputimer.running) {

		struct task_cputime group_sample;



		thread_group_cputimer(tsk, &group_sample);
@@ -1359,6 +1332,11 @@ 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 (tsk->signal->cputimer.running)

		check_process_timers(tsk, &firing);



	/*