linux-stable.git/Documentation/RCU/Design/Data-Structures, branch v4.20

doc: Update removal of RCU-bh/sched update machinery

2018-08-30T17:59:48+00:00

The RCU-bh update API is now defined in terms of that of RCU-bh and
RCU-sched, so this commit updates the documentation accordingly.

In addition, although RCU-sched persists in !PREEMPT kernels, in
the PREEMPT case its update API is now defined in terms of that of
RCU-preempt, so this commit also updates the documentation accordingly.

While in the area, this commit removes the documentation for the
now-obsolete synchronize_rcu_mult() and clarifies the Tasks RCU
documentation.

Signed-off-by: Paul E. McKenney

doc: Improve rcu_dynticks::dynticks documentation

2018-08-29T15:54:30+00:00

The very useful RCU Data-Structures describes that the dynticks counter
of the rcu_dynticks data structure is incremented when we transitions to
or from dynticks-idle mode. However it doesn't mention that it is also
incremented due to transitions to and from user mode which for dynticks
purposes is an extended quiescent state.

I found this with tracing calls to rcu_dynticks_eqs_enter which can also
happen from rcu_user_enter. Lets add this information to the
Data-Structures document.

Signed-off-by: Joel Fernandes (Google) 
Signed-off-by: Paul E. McKenney

doc: Update data-structure documentation for ->gp_seq

2018-07-12T22:38:49+00:00

Signed-off-by: Paul E. McKenney

Merge branches 'cond_resched.2017.12.04a', 'dyntick.2017.11.28a', 'fixes.2017.12.11a', 'srbd.2017.12.05a' and 'torture.2017.12.11a' into HEAD

2017-12-11T17:21:58+00:00

cond_resched.2017.12.04a: Convert cond_resched_rcu_qs() to cond_resched()
dyntick.2017.11.28a: Make RCU dynticks handle interrupts from NMI
fixes.2017.12.11a: Miscellaneous fixes
srbd.2017.12.05a: Remove now-redundant smp_read_barrier_depends()
torture.2017.12.11a: Torture-testing update

doc: Eliminate cond_resched_rcu_qs() in favor of cond_resched()

2017-12-04T18:28:59+00:00

Now that cond_resched() also provides RCU quiescent states when
needed, it can be used in place of cond_resched_rcu_qs().  This
commit therefore documents this change.

Signed-off-by: Paul E. McKenney

doc: Update dyntick-idle design documentation for NMI/irq consolidation

2017-11-28T23:51:22+00:00

Signed-off-by: Paul E. McKenney

Merge branches 'doc.2017.04.12a', 'fixes.2017.04.19a' and 'srcu.2017.04.21a' into HEAD

2017-04-21T13:00:13+00:00

doc.2017.04.12a: Documentation updates
fixes.2017.04.19a: Miscellaneous fixes
srcu.2017.04.21a: Parallelize SRCU callback handling

rcu: Place guard on rcu_all_qs() and rcu_note_context_switch() actions

2017-04-18T18:38:18+00:00

The rcu_all_qs() and rcu_note_context_switch() do a series of checks,
taking various actions to supply RCU with quiescent states, depending
on the outcomes of the various checks.  This is a bit much for scheduling
fastpaths, so this commit creates a separate ->rcu_urgent_qs field in
the rcu_dynticks structure that acts as a global guard for these checks.
Thus, in the common case, rcu_all_qs() and rcu_note_context_switch()
check the ->rcu_urgent_qs field, find it false, and simply return.

Signed-off-by: Paul E. McKenney 
Cc: Peter Zijlstra

rcu: Eliminate flavor scan in rcu_momentary_dyntick_idle()

2017-04-18T18:38:18+00:00

The rcu_momentary_dyntick_idle() function scans the RCU flavors, checking
that one of them still needs a quiescent state before doing an expensive
atomic operation on the ->dynticks counter.  However, this check reduces
overhead only after a rare race condition, and increases complexity.  This
commit therefore removes the scan and the mechanism enabling the scan.

Signed-off-by: Paul E. McKenney

rcu: Pull rcu_qs_ctr into rcu_dynticks structure

2017-04-18T18:38:17+00:00

The rcu_qs_ctr variable is yet another isolated per-CPU variable,
so this commit pulls it into the pre-existing rcu_dynticks per-CPU
structure.

Signed-off-by: Paul E. McKenney