linux.git/Documentation/RCU/Design/Requirements, branch v4.13

rcu: Remove debugfs tracing

2017-06-09T01:52:43+00:00

RCU's debugfs tracing used to be the only reasonable low-level debug
information available, but ftrace and event tracing has since surpassed
the RCU debugfs level of usefulness.  This commit therefore removes
RCU's debugfs tracing.

Signed-off-by: Paul E. McKenney

rcu: Remove SPARSE_RCU_POINTER Kconfig option

2017-06-09T01:52:41+00:00

The sparse-based checking for non-RCU accesses to RCU-protected pointers
has been around for a very long time, and it is now the only type of
sparse-based checking that is optional.  This commit therefore makes
it unconditional.

Reported-by: Ingo Molnar 
Signed-off-by: Paul E. McKenney 
Cc: Fengguang Wu

rcu: Remove nohz_full full-system-idle state machine

2017-06-09T01:52:39+00:00

The NO_HZ_FULL_SYSIDLE full-system-idle capability was added in 2013
by commit 0edd1b1784cb ("nohz_full: Add full-system-idle state machine"),
but has not been used.  This commit therefore removes it.

If it turns out to be needed later, this commit can always be reverted.

Signed-off-by: Paul E. McKenney 
Cc: Frederic Weisbecker 
Cc: Rik van Riel 
Cc: Ingo Molnar 
Acked-by: Linus Torvalds

doc: Take tail recursion into account in RCU requirements

2017-06-08T15:25:34+00:00

This commit classifies tail recursion as an alternative way to write
a loop, with similar limitations.

Signed-off-by: Paul E. McKenney

srcu: Document auto-expediting requirement

2017-06-08T15:25:33+00:00

This commit documents the auto-expediting requirement satisfied by
commits 2da4b2a7fd8d ("srcu: Expedite first synchronize_srcu() when idle")
and 22607d66bbc3 ("srcu: Specify auto-expedite holdoff time").

Signed-off-by: Paul E. McKenney

doc: Update requirements based on recent changes

2017-04-12T15:23:41+00:00

These changes include lighter-weight expedited grace periods, the fact
that expedited grace periods and rcu_barrier() no longer block CPU
hotplug, some HTML font fixups, noting that rcu_barrier() need not wait
for a grace period (even if callbacks are posted), the fact that SRCU
read-side critical sections can be used from offline CPUs, and the fact
that SRCU now maintains per-CPU callback lists.

Signed-off-by: Paul E. McKenney

doc: Synchronous RCU grace periods are now legal throughout boot

2017-04-12T15:23:39+00:00

This commit updates the "Early Boot" section of the RCU requirements
to describe how synchronous RCU grace periods are now legal throughout
the boot process.

Signed-off-by: Paul E. McKenney

doc: Fix RCU requirements typos

2017-01-15T05:29:10+00:00

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

documentation: Present updated RCU guarantee

2016-11-14T18:39:36+00:00

Recent memory-model work deduces the relationships of RCU read-side
critical sections and grace periods based on the relationships of
accesses within a critical section and accesses preceding and following
the grace period.  This commit therefore adds this viewpoint.

Signed-off-by: Paul E. McKenney

documentation: Record reason for rcu_head two-byte alignment

2016-08-22T16:25:33+00:00

There is an assertion in __call_rcu() that checks only the bottom
bit of the rcu_head pointer, rather than the bottom two (as might be
expected for 32-bit systems) or the bottom three (as might be expected
for 64-bit systems).  This choice might be a bit surprising in these days
of ubiquitous 32-bit and 64-bit systems.  This commit therefore records
the reason for this odd alignment check, namely that m68k guarantees
only two-byte alignment despite being a 32-bit architectures.

Signed-off-by: Paul E. McKenney