Re: [RFC PATCH 0/4] sched+mm: Track lazy active mm existence with hazard pointers

[Paul E. McKenney]

On Tue, Oct 01, 2024 at 09:02:01PM -0400, Mathieu Desnoyers wrote:
> Hazard pointers appear to be a good fit for replacing refcount based lazy
> active mm tracking.
> 
> Highlight:
> 
> will-it-scale context_switch1_threads
> 
> nr threads (-t)     speedup
>     24                +3%
>     48               +12%
>     96               +21%
>    192               +28%

Impressive!!!

I have to ask...  Any data for smaller numbers of CPUs?

							Thanx, Paul

> I'm curious to see what the build bots have to say about this.
> 
> This series applies on top of v6.11.1.
> 
> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
> Cc: Nicholas Piggin <npiggin@xxxxxxxxx>
> Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
> Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> Cc: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
> Cc: "Paul E. McKenney" <paulmck@xxxxxxxxxx>
> Cc: Will Deacon <will@xxxxxxxxxx>
> Cc: Boqun Feng <boqun.feng@xxxxxxxxx>
> Cc: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>
> Cc: John Stultz <jstultz@xxxxxxxxxx>
> Cc: Neeraj Upadhyay <Neeraj.Upadhyay@xxxxxxx>
> Cc: Boqun Feng <boqun.feng@xxxxxxxxx>
> Cc: Frederic Weisbecker <frederic@xxxxxxxxxx>
> Cc: Joel Fernandes <joel@xxxxxxxxxxxxxxxxx>
> Cc: Josh Triplett <josh@xxxxxxxxxxxxxxxx>
> Cc: Uladzislau Rezki <urezki@xxxxxxxxx>
> Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
> Cc: Lai Jiangshan <jiangshanlai@xxxxxxxxx>
> Cc: Zqiang <qiang.zhang1211@xxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: Waiman Long <longman@xxxxxxxxxx>
> Cc: Mark Rutland <mark.rutland@xxxxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: Vlastimil Babka <vbabka@xxxxxxx>
> Cc: maged.michael@xxxxxxxxx
> Cc: Mateusz Guzik <mjguzik@xxxxxxxxx>
> Cc: Jonas Oberhauser <jonas.oberhauser@xxxxxxxxxxxxxxx>
> Cc: rcu@xxxxxxxxxxxxxxx
> Cc: linux-mm@xxxxxxxxx
> Cc: lkmm@xxxxxxxxxxxxxxx
> 
> Mathieu Desnoyers (4):
>   compiler.h: Introduce ptr_eq() to preserve address dependency
>   Documentation: RCU: Refer to ptr_eq()
>   hp: Implement Hazard Pointers
>   sched+mm: Use hazard pointers to track lazy active mm existence
> 
>  Documentation/RCU/rcu_dereference.rst |  38 ++++++-
>  Documentation/mm/active_mm.rst        |   9 +-
>  arch/Kconfig                          |  32 ------
>  arch/powerpc/Kconfig                  |   1 -
>  arch/powerpc/mm/book3s64/radix_tlb.c  |  23 +---
>  include/linux/compiler.h              |  63 +++++++++++
>  include/linux/hp.h                    | 154 ++++++++++++++++++++++++++
>  include/linux/mm_types.h              |   3 -
>  include/linux/sched/mm.h              |  71 +++++-------
>  kernel/Makefile                       |   2 +-
>  kernel/exit.c                         |   4 +-
>  kernel/fork.c                         |  47 ++------
>  kernel/hp.c                           |  46 ++++++++
>  kernel/sched/sched.h                  |   8 +-
>  lib/Kconfig.debug                     |  10 --
>  15 files changed, 346 insertions(+), 165 deletions(-)
>  create mode 100644 include/linux/hp.h
>  create mode 100644 kernel/hp.c
> 
> -- 
> 2.39.2