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timer stats: Optimize by adding quick check to avoid function calls
When the kernel is configured with CONFIG_TIMER_STATS but timer stats are runtime disabled we still get calls to __timer_stats_timer_set_start_info which initializes some fields in the corresponding struct timer_list. So add some quick checks in the the timer stats setup functions to avoid function calls to __timer_stats_timer_set_start_info when timer stats are disabled. In an artificial workload that does nothing but playing ping pong with a single tcp packet via loopback this decreases cpu consumption by 1 - 1.5%. This is part of a modified function trace output on SLES11: perl-2497 [00] 28630647177732388 [+ 125]: sk_reset_timer <-tcp_v4_rcv perl-2497 [00] 28630647177732513 [+ 125]: mod_timer <-sk_reset_timer perl-2497 [00] 28630647177732638 [+ 125]: __timer_stats_timer_set_start_info <-mod_timer perl-2497 [00] 28630647177732763 [+ 125]: __mod_timer <-mod_timer perl-2497 [00] 28630647177732888 [+ 125]: __timer_stats_timer_set_start_info <-__mod_timer perl-2497 [00] 28630647177733013 [+ 93]: lock_timer_base <-__mod_timer Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Martin Schwidefsky <schwidefsky@de.ibm.com> Cc: Mustafa Mesanovic <mustafa.mesanovic@de.ibm.com> Cc: Arjan van de Ven <arjan@infradead.org> LKML-Reference: <20090623153811.GA4641@osiris.boeblingen.de.ibm.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
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commit
507e123151
4 changed files with 19 additions and 8 deletions
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@ -21,6 +21,7 @@
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#include <linux/list.h>
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#include <linux/wait.h>
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#include <linux/percpu.h>
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#include <linux/timer.h>
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struct hrtimer_clock_base;
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@ -447,6 +448,8 @@ extern void timer_stats_update_stats(void *timer, pid_t pid, void *startf,
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static inline void timer_stats_account_hrtimer(struct hrtimer *timer)
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{
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if (likely(!timer->start_pid))
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return;
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timer_stats_update_stats(timer, timer->start_pid, timer->start_site,
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timer->function, timer->start_comm, 0);
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}
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@ -456,6 +459,8 @@ extern void __timer_stats_hrtimer_set_start_info(struct hrtimer *timer,
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static inline void timer_stats_hrtimer_set_start_info(struct hrtimer *timer)
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{
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if (likely(!timer_stats_active))
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return;
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__timer_stats_hrtimer_set_start_info(timer, __builtin_return_address(0));
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}
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@ -190,6 +190,8 @@ extern unsigned long get_next_timer_interrupt(unsigned long now);
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*/
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#ifdef CONFIG_TIMER_STATS
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extern int timer_stats_active;
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#define TIMER_STATS_FLAG_DEFERRABLE 0x1
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extern void init_timer_stats(void);
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@ -203,6 +205,8 @@ extern void __timer_stats_timer_set_start_info(struct timer_list *timer,
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static inline void timer_stats_timer_set_start_info(struct timer_list *timer)
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{
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if (likely(!timer_stats_active))
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return;
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__timer_stats_timer_set_start_info(timer, __builtin_return_address(0));
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}
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@ -96,7 +96,7 @@ static DEFINE_MUTEX(show_mutex);
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/*
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* Collection status, active/inactive:
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*/
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static int __read_mostly active;
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int __read_mostly timer_stats_active;
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/*
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* Beginning/end timestamps of measurement:
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@ -242,7 +242,7 @@ void timer_stats_update_stats(void *timer, pid_t pid, void *startf,
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struct entry *entry, input;
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unsigned long flags;
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if (likely(!active))
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if (likely(!timer_stats_active))
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return;
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lock = &per_cpu(lookup_lock, raw_smp_processor_id());
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@ -254,7 +254,7 @@ void timer_stats_update_stats(void *timer, pid_t pid, void *startf,
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input.timer_flag = timer_flag;
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spin_lock_irqsave(lock, flags);
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if (!active)
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if (!timer_stats_active)
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goto out_unlock;
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entry = tstat_lookup(&input, comm);
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@ -290,7 +290,7 @@ static int tstats_show(struct seq_file *m, void *v)
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/*
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* If still active then calculate up to now:
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*/
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if (active)
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if (timer_stats_active)
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time_stop = ktime_get();
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time = ktime_sub(time_stop, time_start);
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@ -368,18 +368,18 @@ static ssize_t tstats_write(struct file *file, const char __user *buf,
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mutex_lock(&show_mutex);
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switch (ctl[0]) {
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case '0':
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if (active) {
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active = 0;
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if (timer_stats_active) {
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timer_stats_active = 0;
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time_stop = ktime_get();
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sync_access();
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}
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break;
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case '1':
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if (!active) {
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if (!timer_stats_active) {
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reset_entries();
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time_start = ktime_get();
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smp_mb();
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active = 1;
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timer_stats_active = 1;
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}
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break;
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default:
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@ -380,6 +380,8 @@ static void timer_stats_account_timer(struct timer_list *timer)
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{
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unsigned int flag = 0;
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if (likely(!timer->start_site))
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return;
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if (unlikely(tbase_get_deferrable(timer->base)))
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flag |= TIMER_STATS_FLAG_DEFERRABLE;
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