[PATCH v7 00/11] rcu: call_rcu() power improvements

From: Joel Fernandes (Google)
Date: Mon Oct 03 2022 - 22:42:26 EST

v7 version of RCU lazy patches based on rcu/next branch.

To facilitate easier merge, I dropped tracing and other patches and just
implemented the new changes. I will post the tracing patches later along with
rcutop as I need to add new tracepoints that Frederic suggested.

Main recent changes:
1. rcu_barrier() wake up only for lazy bypass list.
2. Make all call_rcu() default-lazy and add call_rcu_flush() API.
3. Take care of some callers using call_rcu_flush() API.
4. Several refactorings suggested by Paul/Frederic.
5. New call_rcu() to call_rcu_flush() conversions by Joel/Vlad/Paul.

I am seeing good performance and power with these patches on real ChromeOS x86
asymmetric hardware.

Earlier cover letter with lots of details is here:

List of recent changes:

[ Frederic Weisbec: Program the lazy timer only if WAKE_NOT, since other
deferral levels wake much earlier so for those it is not needed. ]

[ Frederic Weisbec: Use flush flags to keep bypass API code clean. ]

[ Frederic Weisbec: Make rcu_barrier() wake up only if main list empty. ]

[ Frederic Weisbec: Remove extra 'else if' branch in rcu_nocb_try_bypass(). ]

[ Joel: Fix issue where I was not resetting lazy_len after moving it to rdp ]

[ Paul/Thomas/Joel: Make call_rcu() default lazy so users don't mess up. ]

[ Paul/Frederic : Cosmetic changes, split out wakeup of nocb thread. ]

[ Vlad/Joel : More call_rcu -> flush conversions ]

Frederic Weisbecker (1):
rcu: Wake up nocb gp thread on rcu_barrier_entrain()

Joel Fernandes (Google) (7):
rcu: Make call_rcu() lazy to save power
rcu: Refactor code a bit in rcu_nocb_do_flush_bypass()
rcuscale: Add laziness and kfree tests
percpu-refcount: Use call_rcu_flush() for atomic switch
rcu/sync: Use call_rcu_flush() instead of call_rcu
rcu/rcuscale: Use call_rcu_flush() for async reader test
rcu/rcutorture: Use call_rcu_flush() where needed

Uladzislau Rezki (2):
scsi/scsi_error: Use call_rcu_flush() instead of call_rcu()
workqueue: Make queue_rcu_work() use call_rcu_flush()

Vineeth Pillai (1):
rcu: shrinker for lazy rcu

drivers/scsi/scsi_error.c | 2 +-
include/linux/rcupdate.h | 7 ++
kernel/rcu/Kconfig | 8 ++
kernel/rcu/rcu.h | 8 ++
kernel/rcu/rcuscale.c | 67 +++++++++++-
kernel/rcu/rcutorture.c | 16 +--
kernel/rcu/sync.c | 2 +-
kernel/rcu/tiny.c | 2 +-
kernel/rcu/tree.c | 140 +++++++++++++++++--------
kernel/rcu/tree.h | 12 ++-
kernel/rcu/tree_exp.h | 2 +-
kernel/rcu/tree_nocb.h | 213 ++++++++++++++++++++++++++++++++------
kernel/workqueue.c | 2 +-
lib/percpu-refcount.c | 3 +-
14 files changed, 388 insertions(+), 96 deletions(-)