rt-patches/0007-timekeeping-Split-jiffies-seqlock.patch

   1 From 934111e7a727890ecb6b9b72c66c105c21ea23ea Mon Sep 17 00:00:00 2001
   2 From: Thomas Gleixner <tglx@linutronix.de>
   3 Date: Thu, 14 Feb 2013 22:36:59 +0100
   4 Subject: [PATCH 007/366] timekeeping: Split jiffies seqlock
   5
   6 Replace jiffies_lock seqlock with a simple seqcounter and a rawlock so
   7 it can be taken in atomic context on RT.
   8
   9 Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
  10 ---
  11  kernel/time/jiffies.c     |  7 ++++---
  12  kernel/time/tick-common.c | 10 ++++++----
  13  kernel/time/tick-sched.c  | 19 ++++++++++++-------
  14  kernel/time/timekeeping.c |  6 ++++--
  15  kernel/time/timekeeping.h |  3 ++-
  16  5 files changed, 28 insertions(+), 17 deletions(-)
  17
  18 diff --git a/kernel/time/jiffies.c b/kernel/time/jiffies.c
  19 index 347fecf..2ede474 100644
  20 --- a/kernel/time/jiffies.c
  21 +++ b/kernel/time/jiffies.c
  22 @@ -74,7 +74,8 @@ static struct clocksource clocksource_jiffies = {
  23         .max_cycles     = 10,
  24  };
  25
  26 -__cacheline_aligned_in_smp DEFINE_SEQLOCK(jiffies_lock);
  27 +__cacheline_aligned_in_smp DEFINE_RAW_SPINLOCK(jiffies_lock);
  28 +__cacheline_aligned_in_smp seqcount_t jiffies_seq;
  29
  30  #if (BITS_PER_LONG < 64)
  31  u64 get_jiffies_64(void)
  32 @@ -83,9 +84,9 @@ u64 get_jiffies_64(void)
  33         u64 ret;
  34
  35         do {
  36 -               seq = read_seqbegin(&jiffies_lock);
  37 +               seq = read_seqcount_begin(&jiffies_seq);
  38                 ret = jiffies_64;
  39 -       } while (read_seqretry(&jiffies_lock, seq));
  40 +       } while (read_seqcount_retry(&jiffies_seq, seq));
  41         return ret;
  42  }
  43  EXPORT_SYMBOL(get_jiffies_64);
  44 diff --git a/kernel/time/tick-common.c b/kernel/time/tick-common.c
  45 index 4fcd99e..5a47f2e 100644
  46 --- a/kernel/time/tick-common.c
  47 +++ b/kernel/time/tick-common.c
  48 @@ -79,13 +79,15 @@ int tick_is_oneshot_available(void)
  49  static void tick_periodic(int cpu)
  50  {
  51         if (tick_do_timer_cpu == cpu) {
  52 -               write_seqlock(&jiffies_lock);
  53 +               raw_spin_lock(&jiffies_lock);
  54 +               write_seqcount_begin(&jiffies_seq);
  55
  56                 /* Keep track of the next tick event */
  57                 tick_next_period = ktime_add(tick_next_period, tick_period);
  58
  59                 do_timer(1);
  60 -               write_sequnlock(&jiffies_lock);
  61 +               write_seqcount_end(&jiffies_seq);
  62 +               raw_spin_unlock(&jiffies_lock);
  63                 update_wall_time();
  64         }
  65
  66 @@ -157,9 +159,9 @@ void tick_setup_periodic(struct clock_event_device *dev, int broadcast)
  67                 ktime_t next;
  68
  69                 do {
  70 -                       seq = read_seqbegin(&jiffies_lock);
  71 +                       seq = read_seqcount_begin(&jiffies_seq);
  72                         next = tick_next_period;
  73 -               } while (read_seqretry(&jiffies_lock, seq));
  74 +               } while (read_seqcount_retry(&jiffies_seq, seq));
  75
  76                 clockevents_switch_state(dev, CLOCK_EVT_STATE_ONESHOT);
  77
  78 diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
  79 index 22c57e1..9579f79 100644
  80 --- a/kernel/time/tick-sched.c
  81 +++ b/kernel/time/tick-sched.c
  82 @@ -62,7 +62,8 @@ static void tick_do_update_jiffies64(ktime_t now)
  83                 return;
  84
  85         /* Reevalute with jiffies_lock held */
  86 -       write_seqlock(&jiffies_lock);
  87 +       raw_spin_lock(&jiffies_lock);
  88 +       write_seqcount_begin(&jiffies_seq);
  89
  90         delta = ktime_sub(now, last_jiffies_update);
  91         if (delta.tv64 >= tick_period.tv64) {
  92 @@ -85,10 +86,12 @@ static void tick_do_update_jiffies64(ktime_t now)
  93                 /* Keep the tick_next_period variable up to date */
  94                 tick_next_period = ktime_add(last_jiffies_update, tick_period);
  95         } else {
  96 -               write_sequnlock(&jiffies_lock);
  97 +               write_seqcount_end(&jiffies_seq);
  98 +               raw_spin_unlock(&jiffies_lock);
  99                 return;
 100         }
 101 -       write_sequnlock(&jiffies_lock);
 102 +       write_seqcount_end(&jiffies_seq);
 103 +       raw_spin_unlock(&jiffies_lock);
 104         update_wall_time();
 105  }
 106
 107 @@ -99,12 +102,14 @@ static ktime_t tick_init_jiffy_update(void)
 108  {
 109         ktime_t period;
 110
 111 -       write_seqlock(&jiffies_lock);
 112 +       raw_spin_lock(&jiffies_lock);
 113 +       write_seqcount_begin(&jiffies_seq);
 114         /* Did we start the jiffies update yet ? */
 115         if (last_jiffies_update.tv64 == 0)
 116                 last_jiffies_update = tick_next_period;
 117         period = last_jiffies_update;
 118 -       write_sequnlock(&jiffies_lock);
 119 +       write_seqcount_end(&jiffies_seq);
 120 +       raw_spin_unlock(&jiffies_lock);
 121         return period;
 122  }
 123
 124 @@ -578,10 +583,10 @@ static ktime_t tick_nohz_stop_sched_tick(struct tick_sched *ts,
 125
 126         /* Read jiffies and the time when jiffies were updated last */
 127         do {
 128 -               seq = read_seqbegin(&jiffies_lock);
 129 +               seq = read_seqcount_begin(&jiffies_seq);
 130                 basemono = last_jiffies_update.tv64;
 131                 basejiff = jiffies;
 132 -       } while (read_seqretry(&jiffies_lock, seq));
 133 +       } while (read_seqcount_retry(&jiffies_seq, seq));
 134         ts->last_jiffies = basejiff;
 135
 136         if (rcu_needs_cpu(basemono, &next_rcu) ||
 137 diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
 138 index 9a1092b..a963d9e 100644
 139 --- a/kernel/time/timekeeping.c
 140 +++ b/kernel/time/timekeeping.c
 141 @@ -2072,8 +2072,10 @@ EXPORT_SYMBOL(hardpps);
 142   */
 143  void xtime_update(unsigned long ticks)
 144  {
 145 -       write_seqlock(&jiffies_lock);
 146 +       raw_spin_lock(&jiffies_lock);
 147 +       write_seqcount_begin(&jiffies_seq);
 148         do_timer(ticks);
 149 -       write_sequnlock(&jiffies_lock);
 150 +       write_seqcount_end(&jiffies_seq);
 151 +       raw_spin_unlock(&jiffies_lock);
 152         update_wall_time();
 153  }
 154 diff --git a/kernel/time/timekeeping.h b/kernel/time/timekeeping.h
 155 index 704f595..763a3e5 100644
 156 --- a/kernel/time/timekeeping.h
 157 +++ b/kernel/time/timekeeping.h
 158 @@ -19,7 +19,8 @@ extern void timekeeping_resume(void);
 159  extern void do_timer(unsigned long ticks);
 160  extern void update_wall_time(void);
 161
 162 -extern seqlock_t jiffies_lock;
 163 +extern raw_spinlock_t jiffies_lock;
 164 +extern seqcount_t jiffies_seq;
 165
 166  #define CS_NAME_LEN    32
 167
 168 --
 169 1.9.1
 170