aboutsummaryrefslogtreecommitdiff
path: root/include
diff options
context:
space:
mode:
authorPeter Xu <peterx@redhat.com>2019-06-28 18:59:42 +0800
committerThomas Gleixner <tglx@linutronix.de>2019-07-07 11:50:03 +0200
commit28ef2db8866495150e4260773fead8313f1a5625 (patch)
treeb5eecff402061ee6fe7cb26b3c9a50543bfc2381 /include
parentdd2cb348613b44f9d948b068775e159aad298599 (diff)
download96b-common-28ef2db8866495150e4260773fead8313f1a5625.tar.gz
timer: Document TIMER_PINNED
The flag hints the user that the pinned timers will always be run on a static CPU (because that should be what "pinned" means...) but that's not the truth, at least with the current implementation. For example, currently if a pinned timer is set up but later mod_timer() upon the pinned timer is invoked, mod_timer() will still try to queue the timer on the current processor and migrate the timer if necessary. Document it a bit with the definition of TIMER_PINNED so that all future users will use it correctly. Signed-off-by: Peter Xu <peterx@redhat.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Cc: Marcelo Tosatti <mtosatti@redhat.com> Cc: Luiz Capitulino <lcapitulino@redhat.com> Link: https://lkml.kernel.org/r/20190628105942.14131-1-peterx@redhat.com
Diffstat (limited to 'include')
-rw-r--r--include/linux/timer.h27
1 files changed, 19 insertions, 8 deletions
diff --git a/include/linux/timer.h b/include/linux/timer.h
index 7b066fd38248..282e4f2a532a 100644
--- a/include/linux/timer.h
+++ b/include/linux/timer.h
@@ -36,19 +36,30 @@ struct timer_list {
#define __TIMER_LOCKDEP_MAP_INITIALIZER(_kn)
#endif
-/*
- * A deferrable timer will work normally when the system is busy, but
- * will not cause a CPU to come out of idle just to service it; instead,
- * the timer will be serviced when the CPU eventually wakes up with a
- * subsequent non-deferrable timer.
+/**
+ * @TIMER_DEFERRABLE: A deferrable timer will work normally when the
+ * system is busy, but will not cause a CPU to come out of idle just
+ * to service it; instead, the timer will be serviced when the CPU
+ * eventually wakes up with a subsequent non-deferrable timer.
*
- * An irqsafe timer is executed with IRQ disabled and it's safe to wait for
- * the completion of the running instance from IRQ handlers, for example,
- * by calling del_timer_sync().
+ * @TIMER_IRQSAFE: An irqsafe timer is executed with IRQ disabled and
+ * it's safe to wait for the completion of the running instance from
+ * IRQ handlers, for example, by calling del_timer_sync().
*
* Note: The irq disabled callback execution is a special case for
* workqueue locking issues. It's not meant for executing random crap
* with interrupts disabled. Abuse is monitored!
+ *
+ * @TIMER_PINNED: A pinned timer will not be affected by any timer
+ * placement heuristics (like, NOHZ) and will always expire on the CPU
+ * on which the timer was enqueued.
+ *
+ * Note: Because enqueuing of timers can migrate the timer from one
+ * CPU to another, pinned timers are not guaranteed to stay on the
+ * initialy selected CPU. They move to the CPU on which the enqueue
+ * function is invoked via mod_timer() or add_timer(). If the timer
+ * should be placed on a particular CPU, then add_timer_on() has to be
+ * used.
*/
#define TIMER_CPUMASK 0x0003FFFF
#define TIMER_MIGRATING 0x00040000