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| author | Peter Xu <peterx@redhat.com> | 2019-06-28 18:59:42 +0800 |
|---|---|---|
| committer | Thomas Gleixner <tglx@linutronix.de> | 2019-07-07 11:50:03 +0200 |
| commit | 28ef2db8866495150e4260773fead8313f1a5625 (patch) | |
| tree | b5eecff402061ee6fe7cb26b3c9a50543bfc2381 /include/linux/timer.h | |
| parent | dd2cb348613b44f9d948b068775e159aad298599 (diff) | |
| download | lwn-28ef2db8866495150e4260773fead8313f1a5625.tar.gz lwn-28ef2db8866495150e4260773fead8313f1a5625.zip | |
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/linux/timer.h')
| -rw-r--r-- | include/linux/timer.h | 27 |
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 |