linux-kernel - [patch 28/44] posix-cpu-timers: Simplify timer queueing

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Date:   Mon, 19 Aug 2019 16:32:09 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     Oleg Nesterov <oleg@...hat.com>, Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        John Stultz <john.stultz@...aro.org>,
        Frederic Weisbecker <fweisbec@...il.com>,
        Anna-Maria Behnsen <anna-maria@...utronix.de>
Subject: [patch 28/44] posix-cpu-timers: Simplify timer queueing

Now that the expiry cache can be accessed as an array, the per clock
checking can be reduced to just comparing the corresponding array elements.

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
---
 kernel/time/posix-cpu-timers.c |   57 +++++++++++++++--------------------------
 1 file changed, 22 insertions(+), 35 deletions(-)

--- a/kernel/time/posix-cpu-timers.c
+++ b/kernel/time/posix-cpu-timers.c
@@ -449,20 +449,20 @@ static inline int expires_gt(u64 expires
  */
 static void arm_timer(struct k_itimer *timer)
 {
+	struct cpu_timer_list *const nt = &timer->it.cpu;
+	int clkidx = CPUCLOCK_WHICH(timer->it_clock);
+	u64 *cpuexp, newexp = timer->it.cpu.expires;
 	struct task_struct *p = timer->it.cpu.task;
 	struct list_head *head, *listpos;
-	struct task_cputime *cputime_expires;
-	struct cpu_timer_list *const nt = &timer->it.cpu;
 	struct cpu_timer_list *next;
 
 	if (CPUCLOCK_PERTHREAD(timer->it_clock)) {
-		head = p->posix_cputimers.cpu_timers;
-		cputime_expires = &p->posix_cputimers.cputime_expires;
+		head = p->posix_cputimers.cpu_timers + clkidx;
+		cpuexp = p->posix_cputimers.expiries + clkidx;
 	} else {
-		head = p->signal->posix_cputimers.cpu_timers;
-		cputime_expires = &p->signal->posix_cputimers.cputime_expires;
+		head = p->signal->posix_cputimers.cpu_timers + clkidx;
+		cpuexp = p->signal->posix_cputimers.expiries + clkidx;
 	}
-	head += CPUCLOCK_WHICH(timer->it_clock);
 
 	listpos = head;
 	list_for_each_entry(next, head, entry) {
@@ -472,35 +472,22 @@ static void arm_timer(struct k_itimer *t
 	}
 	list_add(&nt->entry, listpos);
 
-	if (listpos == head) {
-		u64 exp = nt->expires;
+	if (listpos != head)
+		return;
 
-		/*
-		 * We are the new earliest-expiring POSIX 1.b timer, hence
-		 * need to update expiration cache. Take into account that
-		 * for process timers we share expiration cache with itimers
-		 * and RLIMIT_CPU and for thread timers with RLIMIT_RTTIME.
-		 */
-
-		switch (CPUCLOCK_WHICH(timer->it_clock)) {
-		case CPUCLOCK_PROF:
-			if (expires_gt(cputime_expires->prof_exp, exp))
-				cputime_expires->prof_exp = exp;
-			break;
-		case CPUCLOCK_VIRT:
-			if (expires_gt(cputime_expires->virt_exp, exp))
-				cputime_expires->virt_exp = exp;
-			break;
-		case CPUCLOCK_SCHED:
-			if (expires_gt(cputime_expires->sched_exp, exp))
-				cputime_expires->sched_exp = exp;
-			break;
-		}
-		if (CPUCLOCK_PERTHREAD(timer->it_clock))
-			tick_dep_set_task(p, TICK_DEP_BIT_POSIX_TIMER);
-		else
-			tick_dep_set_signal(p->signal, TICK_DEP_BIT_POSIX_TIMER);
-	}
+	/*
+	 * We are the new earliest-expiring POSIX 1.b timer, hence
+	 * need to update expiration cache. Take into account that
+	 * for process timers we share expiration cache with itimers
+	 * and RLIMIT_CPU and for thread timers with RLIMIT_RTTIME.
+	 */
+	if (expires_gt(*cpuexp, newexp))
+		*cpuexp = newexp;
+
+	if (CPUCLOCK_PERTHREAD(timer->it_clock))
+		tick_dep_set_task(p, TICK_DEP_BIT_POSIX_TIMER);
+	else
+		tick_dep_set_signal(p->signal, TICK_DEP_BIT_POSIX_TIMER);
 }
 
 /*