[GIT PULL] nohz: Tick dependency mask v2

[Frederic Weisbecker]

On Tue, Feb 16, 2016 at 09:03:45AM +0100, Ingo Molnar wrote:
> 
> 
> So I think it would be useful to name this in a way the expresses that this is a 
> mask.
> 
> 'tick_dep_mask' or so?

[...]

> >  
> > +enum tick_dependency_bit {
> 
> s/tick_dep_bits
> 
> > +	TICK_POSIX_TIMER_BIT	= 0,
> > +	TICK_PERF_EVENTS_BIT	= 1,
> > +	TICK_SCHED_BIT		= 2,
> > +	TICK_CLOCK_UNSTABLE_BIT	= 3
> 
> s/TICK_DEP_BIT_...
> 
> > +};
> > +
> > +#define TICK_POSIX_TIMER_MASK		(1 << TICK_POSIX_TIMER_BIT)
> > +#define TICK_PERF_EVENTS_MASK		(1 << TICK_PERF_EVENTS_BIT)
> > +#define TICK_SCHED_MASK			(1 << TICK_SCHED_BIT)
> > +#define TICK_CLOCK_UNSTABLE_MASK	(1 << TICK_CLOCK_UNSTABLE_BIT)
> 
> So I'd rename this to:
> 
> #define TICK_DEP_MASK_POSIX_TIMER	(1 << TICK_POSIX_TIMER_BIT)
> #define TICK_DEP_MASK_PERF_EVENTS	(1 << TICK_PERF_EVENTS_BIT)
> #define TICK_DEP_MASK_SCHED		(1 << TICK_SCHED_BIT)
> #define TICK_DEP_MASK_CLOCK_UNSTABLE	(1 << TICK_CLOCK_UNSTABLE_BIT)
> 
> i.e. the 'tick_dep' and 'TICK_DEP' nomenclature would be used throughout the code 
> and the pattern would be easy to grep for.
> 
> > +extern void tick_nohz_set_dep(enum tick_dependency_bit bit);
> > +extern void tick_nohz_clear_dep(enum tick_dependency_bit bit);
> > +extern void tick_nohz_set_dep_cpu(int cpu, enum tick_dependency_bit bit);
> > +extern void tick_nohz_clear_dep_cpu(int cpu, enum tick_dependency_bit bit);
> > +extern void tick_nohz_set_dep_task(struct task_struct *tsk,
> > +				   enum tick_dependency_bit bit);
> > +extern void tick_nohz_clear_dep_task(struct task_struct *tsk,
> > +				     enum tick_dependency_bit bit);
> > +extern void tick_nohz_set_dep_signal(struct signal_struct *signal,
> > +				     enum tick_dependency_bit bit);
> > +extern void tick_nohz_clear_dep_signal(struct signal_struct *signal,
> > +				       enum tick_dependency_bit bit);
> 
> Ditto, please rename it all to:
> 
> 	tick_dep_set()
> 	tick_dep_clear()
> 	tick_dep_set_cpu()
> 	tick_dep_clear_cpu()
> 	tick_dep_set_task()
> 	...

Ok, I fixed all the above.

> 
> also, please don't line-break function prototypes, it only makes the result harder 
> to read.

I couldn't fix that though, I'm limited by the 80 columns.


If you're ok with it, please pull the branch:

git://git.kernel.org/pub/scm/linux/kernel/git/frederic/linux-dynticks.git
	timers/core-v9

HEAD: 4f49b90abb4aca6fe677c95fc352fd0674d489bd

--- Summary ---

Currently in nohz full configs, the tick dependency is checked
asynchronously by nohz code from interrupt and context switch for each
concerned subsystem with a set of function provided by these. Such
functions are made of many conditions and details that can be heavyweight
as they are called on fastpath: sched_can_stop_tick(),
posix_cpu_timer_can_stop_tick(), perf_event_can_stop_tick()...

Thomas suggested a few month ago to make that tick dependency check
synchronous. Instead of checking subsystems details from each interrupt
to guess if the tick can be stopped, every subsystem that may have a tick
dependency should set itself a flag specifying the state of that
dependency. This way we can verify if we can stop the tick with a single
lightweight mask check on fast path.

This conversion from a pull to a push model to implement tick dependency
is the core feature of this patchset that is split into:

* Nohz wide kick simplification
* Improve nohz tracing
* Introduce tick dependency mask
* Migrate scheduler, posix timers, perf events and sched clock tick
  dependencies to the tick dependency mask.

Thanks!