linux-kernel - Re: [PATCH v9 00/13] rcu: call

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Message-ID: <20221017140726.GG5600@paulmck-ThinkPad-P17-Gen-1>
Date:   Mon, 17 Oct 2022 07:07:26 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Joel Fernandes <joel@...lfernandes.org>
Cc:     rcu@...r.kernel.org, linux-kernel@...r.kernel.org,
        frederic@...nel.org
Subject: Re: [PATCH v9 00/13] rcu: call_rcu() power improvements

On Mon, Oct 17, 2022 at 09:47:00AM -0400, Joel Fernandes wrote:
> On Mon, Oct 17, 2022 at 9:37 AM Paul E. McKenney <paulmck@...nel.org> wrote:
> >
> > On Sun, Oct 16, 2022 at 04:22:52PM +0000, Joel Fernandes (Google) wrote:
> > > v9 version of RCU lazy patches based on rcu/next branch.
> > >  Only change since v8 is this discussion:
> > >  https://lore.kernel.org/rcu/20221011180142.2742289-1-joel@joelfernandes.org/T/#m8eff15110477f3430b3b02561b66f7b0d34a73b0
> > >
> > > 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:
> > > https://lore.kernel.org/all/20220901221720.1105021-1-joel@joelfernandes.org/
> > >
> [...]
> >
> > Very good, thank you all!
> >
> > I have pulled these in for further review and testing.
> >
> > I am holding off on the last one ("rcu/debug: Add wake-up debugging for
> > lazy callbacks") for the immediate future, but let's see how it goes.
> 
> Thanks! And nice timing with RCU just turning 20 years old ;-)

Yes, 20 years old, but with the qualifier "in the Linux kernel".  ;-)

RCU was in DYNIX/ptx for almost ten years prior to that.  And mechanisms
vaguely resembling RCU go back to Kung's and Lehman's 1980 paper entitled
"Concurrent Manipulation of Binary Search Trees".  And maybe farther,
but that is the oldest citation I know of.

							Thanx, Paul

>  - Joel
> 
> 
> 
> 
> >
> >                                                         Thanx, Paul
> >
> > > Frederic Weisbecker (1):
> > > rcu: Fix missing nocb gp wake on rcu_barrier()
> > >
> > > Joel Fernandes (Google) (9):
> > > 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
> > > rxrpc: Use call_rcu_flush() instead of call_rcu()
> > > rcu/debug: Add wake-up debugging for lazy callbacks
> > >
> > > 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        |  15 +++
> > > kernel/rcu/lazy-debug.h   | 154 +++++++++++++++++++++++++++
> > > kernel/rcu/rcu.h          |   8 ++
> > > kernel/rcu/rcuscale.c     |  70 +++++++++++-
> > > kernel/rcu/rcutorture.c   |  16 +--
> > > kernel/rcu/sync.c         |   2 +-
> > > kernel/rcu/tiny.c         |   2 +-
> > > kernel/rcu/tree.c         | 149 ++++++++++++++++++--------
> > > kernel/rcu/tree.h         |  12 ++-
> > > kernel/rcu/tree_exp.h     |   2 +-
> > > kernel/rcu/tree_nocb.h    | 217 ++++++++++++++++++++++++++++++++------
> > > kernel/workqueue.c        |   2 +-
> > > lib/percpu-refcount.c     |   3 +-
> > > net/rxrpc/conn_object.c   |   2 +-
> > > 16 files changed, 565 insertions(+), 98 deletions(-)
> > > create mode 100644 kernel/rcu/lazy-debug.h
> > >
> > > --
> > > 2.38.0.413.g74048e4d9e-goog
> > >