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

Thomas Gleixner
2019-08-19T15:46:07Z

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@linutronix.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);
}

/*