[PATCH RFC 0/9] Reduce ratelimit's false-positive misses

[Paul E. McKenney]

Hello!

This RFC series replaces open-coded uses of the ratelimit_state structure
with formal APIs, counts all rate-limit misses, replaces jiffies=0
special case with a flag, provides a ___ratelimit() lockless fastpath
to (almost) eliminate false-positive misses, and adds a simple test.
The lockless fastpath also provides a 10-20% speedup on my x86 laptop,
though your mileage may vary.

The key point of this series is the reduction of false-positive misses.
Patches 4-7 move in this direction within the fully locked confines of
the current design, and patch 8 introduces the lockless fastpath.

The individual patches are as follows:

1.	Create functions to handle ratelimit_state internals.

2.	random: Avoid open-coded use of ratelimit_state structure's
	->missed field.

3.	drm/i915: Avoid open-coded use of ratelimit_state structure's
	->missed field.

4.	drm/amd/pm: Avoid open-coded use of ratelimit_state structure's
	internals.

5.	Convert the ->missed field to atomic_t.

6.	Count misses due to lock contention.

7.	Avoid jiffies=0 special case.

8.	Reduce ratelimit's false-positive misses.

9.	Add trivial kunit test for ratelimit.

						Thanx, Paul

------------------------------------------------------------------------

 b/drivers/char/random.c              |    9 -
 b/drivers/gpu/drm/amd/pm/amdgpu_pm.c |   11 --
 b/drivers/gpu/drm/i915/i915_perf.c   |    8 -
 b/include/linux/ratelimit.h          |   40 ++++++-
 b/include/linux/ratelimit_types.h    |    2 
 b/lib/Kconfig.debug                  |   11 ++
 b/lib/Makefile                       |    1 
 b/lib/ratelimit.c                    |    8 -
 b/lib/test_ratelimit.c               |   77 ++++++++++++++
 include/linux/ratelimit.h            |   13 --
 include/linux/ratelimit_types.h      |    4 
 lib/ratelimit.c                      |  186 +++++++++++++++++++++++++++--------
 12 files changed, 296 insertions(+), 74 deletions(-)