highres/dyntick: prevent xtime lock contention

While the !highres/!dyntick code assigns the duty of the do_timer() call to
one specific CPU, this was dropped in the highres/dyntick part during
development.

Steven Rostedt discovered the xtime lock contention on highres/dyntick due
to several CPUs trying to update jiffies.

Add the single CPU assignement back.  In the dyntick case this needs to be
handled carefully, as the CPU which has the do_timer() duty must drop the
assignement and let it be grabbed by another CPU, which is active.
Otherwise the do_timer() calls would not happen during the long sleep.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Ingo Molnar <mingo@elte.hu>
Cc: Steven Rostedt <rostedt@goodmis.org>
Acked-by: Mark Lord <mlord@pobox.com>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 7 insertions, 1 deletions

diff --git a/kernel/time/tick-common.c b/kernel/time/tick-common.c
index bfda3f7f0716..a96ec9ab3454 100644
--- a/kernel/time/tick-common.c
+++ b/kernel/time/tick-common.c
@@ -31,7 +31,7 @@ DEFINE_PER_CPU(struct tick_device, tick_cpu_device);
  */
 ktime_t tick_next_period;
 ktime_t tick_period;
-static int tick_do_timer_cpu = -1;
+int tick_do_timer_cpu __read_mostly = -1;
 DEFINE_SPINLOCK(tick_device_lock);
 
 /*
@@ -295,6 +295,12 @@ static void tick_shutdown(unsigned int *cpup)
                 clockevents_exchange_device(dev, NULL);
                 td->evtdev = NULL;
         }
+        /* Transfer the do_timer job away from this cpu */
+        if (*cpup == tick_do_timer_cpu) {
+                int cpu = first_cpu(cpu_online_map);
+
+                tick_do_timer_cpu = (cpu != NR_CPUS) ? cpu : -1;
+        }
         spin_unlock_irqrestore(&tick_device_lock, flags);
 }