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tick: Nohz: Rework next timer evaluation

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The evaluation of the next timer in the nohz code is based on jiffies
while all the tick internals are nano seconds based. We have also to
convert hrtimer nanoseconds to jiffies in the !highres case. That's
just wrong and introduces interesting corner cases.

Turn it around and convert the next timer wheel timer expiry and the
rcu event to clock monotonic and base all calculations on
nanoseconds. That identifies the case where no timer is pending
clearly with an absolute expiry value of KTIME_MAX.

Makes the code more readable and gets rid of the jiffies magic in the
nohz code.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Cc: Preeti U Murthy <preeti@linux.vnet.ibm.com>
Cc: Viresh Kumar <viresh.kumar@linaro.org>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Lai Jiangshan <laijs@cn.fujitsu.com>
Cc: John Stultz <john.stultz@linaro.org>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Link: http://lkml.kernel.org/r/20150414203502.184198593@linutronix.de
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
This commit is contained in:
Thomas Gleixner 2015-04-14 21:08:58 +00:00
parent 157d29e101
commit c1ad348b45
11 changed files with 108 additions and 127 deletions
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6
include/linux/rcupdate.h
View file

@ -44,6 +44,8 @@
#include <linux/debugobjects.h>
#include <linux/bug.h>
#include <linux/compiler.h>
#include <linux/ktime.h>
#include <asm/barrier.h>
extern int rcu_expedited; /* for sysctl */
@ -1154,9 +1156,9 @@ static inline notrace void rcu_read_unlock_sched_notrace(void)
__kfree_rcu(&((ptr)->rcu_head), offsetof(typeof(*(ptr)), rcu_head))
#if defined(CONFIG_TINY_RCU) || defined(CONFIG_RCU_NOCB_CPU_ALL)
static inline int rcu_needs_cpu(unsigned long *delta_jiffies)
static inline int rcu_needs_cpu(u64 basemono, u64 *nextevt)
{
*delta_jiffies = ULONG_MAX;
*nextevt = KTIME_MAX;
return 0;
}
#endif /* #if defined(CONFIG_TINY_RCU) || defined(CONFIG_RCU_NOCB_CPU_ALL) */