linux-toradex.git/include/linux/rcupdate.h, branch v3.12.8

nohz_full: Add full-system-idle state machine

2013-08-31T21:43:50+00:00

This commit adds the state machine that takes the per-CPU idle data
as input and produces a full-system-idle indication as output.  This
state machine is driven out of RCU's quiescent-state-forcing
mechanism, which invokes rcu_sysidle_check_cpu() to collect per-CPU
idle state and then rcu_sysidle_report() to drive the state machine.

The full-system-idle state is sampled using rcu_sys_is_idle(), which
also drives the state machine if RCU is idle (and does so by forcing
RCU to become non-idle).  This function returns true if all but the
timekeeping CPU (tick_do_timer_cpu) are idle and have been idle long
enough to avoid memory contention on the full_sysidle_state state
variable.  The rcu_sysidle_force_exit() may be called externally
to reset the state machine back into non-idle state.

For large systems the state machine is driven out of RCU's
force-quiescent-state logic, which provides good scalability at the price
of millisecond-scale latencies on the transition to full-system-idle
state.  This is not so good for battery-powered systems, which are usually
small enough that they don't need to care about scalability, but which
do care deeply about energy efficiency.  Small systems therefore drive
the state machine directly out of the idle-entry code.  The number of
CPUs in a "small" system is defined by a new NO_HZ_FULL_SYSIDLE_SMALL
Kconfig parameter, which defaults to 8.  Note that this is a build-time
definition.

Signed-off-by: Paul E. McKenney 
Cc: Frederic Weisbecker 
Cc: Steven Rostedt 
Cc: Lai Jiangshan 
[ paulmck: Use true and false for boolean constants per Lai Jiangshan. ]
Reviewed-by: Josh Triplett 
[ paulmck: Simplify logic and provide better comments for memory barriers,
  based on review comments and questions by Lai Jiangshan. ]

rcu: Eliminate unused APIs intended for adaptive ticks

2013-08-19T01:06:44+00:00

The rcu_user_enter_after_irq() and rcu_user_exit_after_irq()
functions were intended for use by adaptive ticks, but changes
in implementation have rendered them unnecessary.  This commit
therefore removes them.

Reported-by: Frederic Weisbecker 
Signed-off-by: Paul E. McKenney 
Reviewed-by: Josh Triplett

rcu: Add const annotation to char * for RCU tracepoints and functions

2013-07-29T21:07:49+00:00

All the RCU tracepoints and functions that reference char pointers do
so with just 'char *' even though they do not modify the contents of
the string itself. This will cause warnings if a const char * is used
in one of these functions.

The RCU tracepoints store the pointer to the string to refer back to them
when the trace output is displayed. As this can be minutes, hours or
even days later, those strings had better be constant.

This change also opens the door to allow the RCU tracepoint strings and
their addresses to be exported so that userspace tracing tools can
translate the contents of the pointers of the RCU tracepoints.

Signed-off-by: Steven Rostedt

rcu: Shrink TINY_RCU by moving exit_rcu()

2013-06-10T20:45:52+00:00

Now that TINY_PREEMPT_RCU is no more, exit_rcu() is always an empty
function.  But if TINY_RCU is going to have an empty function, it should
be in include/linux/rcutiny.h, where it does not bloat the kernel.
This commit therefore moves exit_rcu() out of kernel/rcupdate.c to
kernel/rcutree_plugin.h, and places a static inline empty function in
include/linux/rcutiny.h in order to shrink TINY_RCU a bit.

Signed-off-by: Paul E. McKenney 
Reviewed-by: Josh Triplett

rcu: Simplify RCU_TINY RCU callback invocation

2013-06-10T20:45:51+00:00

TINY_PREEMPT_RCU could use a kthread to handle RCU callback invocation,
which required an API to abstract kthread vs. softirq invocation.
Now that TINY_PREEMPT_RCU is no longer with us, this commit retires
this API in favor of direct use of the relevant softirq primitives.

Signed-off-by: Paul E. McKenney 
Reviewed-by: Josh Triplett

rcu: Remove TINY_PREEMPT_RCU

2013-06-10T20:45:49+00:00

TINY_PREEMPT_RCU adds significant code and complexity, but does not
offer commensurate benefits.  People currently using TINY_PREEMPT_RCU
can get much better memory footprint with TINY_RCU, or, if they really
need preemptible RCU, they can use TREE_PREEMPT_RCU with a relatively
minor degradation in memory footprint.  Please note that this move
has been widely publicized on LKML (https://lkml.org/lkml/2012/11/12/545)
and on LWN (http://lwn.net/Articles/541037/).

This commit therefore removes TINY_PREEMPT_RCU.

Signed-off-by: Paul E. McKenney 
[ paulmck: Updated to eliminate #else in rcutiny.h as suggested by Josh ]
Reviewed-by: Josh Triplett

rcu: Add _notrace variation of rcu_dereference_raw() and hlist_for_each_entry_rcu()

2013-05-29T02:47:13+00:00

As rcu_dereference_raw() under RCU debug config options can add quite a
bit of checks, and that tracing uses rcu_dereference_raw(), these checks
happen with the function tracer. The function tracer also happens to trace
these debug checks too. This added overhead can livelock the system.

Add a new interface to RCU for both rcu_dereference_raw_notrace() as well
as hlist_for_each_entry_rcu_notrace() as the hlist iterator uses the
rcu_dereference_raw() as well, and is used a bit with the function tracer.

Link: http://lkml.kernel.org/r/20130528184209.304356745@goodmis.org

Acked-by: Paul E. McKenney 
Signed-off-by: Steven Rostedt

Merge commit '8700c95adb03' into timers/nohz

2013-05-02T15:54:19+00:00

The full dynticks tree needs the latest RCU and sched
upstream updates in order to fix some dependencies.

Merge a common upstream merge point that has these
updates.

Conflicts:
	include/linux/perf_event.h
	kernel/rcutree.h
	kernel/rcutree_plugin.h

Signed-off-by: Frederic Weisbecker

nohz: Ensure full dynticks CPUs are RCU nocbs

2013-04-19T11:54:04+00:00

We need full dynticks CPU to also be RCU nocb so
that we don't have to keep the tick to handle RCU
callbacks.

Make sure the range passed to nohz_full= boot
parameter is a subset of rcu_nocbs=

The CPUs that fail to meet this requirement will be
excluded from the nohz_full range. This is checked
early in boot time, before any CPU has the opportunity
to stop its tick.

Suggested-by: Steven Rostedt 
Reviewed-by: Paul E. McKenney 
Signed-off-by: Frederic Weisbecker 
Cc: Andrew Morton 
Cc: Chris Metcalf 
Cc: Christoph Lameter 
Cc: Geoff Levand 
Cc: Gilad Ben Yossef 
Cc: Hakan Akkan 
Cc: Ingo Molnar 
Cc: Kevin Hilman 
Cc: Li Zhong 
Cc: Paul E. McKenney 
Cc: Paul Gortmaker 
Cc: Peter Zijlstra 
Cc: Steven Rostedt 
Cc: Thomas Gleixner

rcu: Make RCU_FAST_NO_HZ take advantage of numbered callbacks

2013-03-26T15:04:51+00:00

Because RCU callbacks are now associated with the number of the grace
period that they must wait for, CPUs can now take advance callbacks
corresponding to grace periods that ended while a given CPU was in
dyntick-idle mode.  This eliminates the need to try forcing the RCU
state machine while entering idle, thus reducing the CPU intensiveness
of RCU_FAST_NO_HZ, which should increase its energy efficiency.

Signed-off-by: Paul E. McKenney 
Signed-off-by: Paul E. McKenney