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

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Message-ID: <cfcf9c05-c639-4757-a3ac-6504d154cdfe@paulmck-laptop>
Date: Wed, 2 Oct 2024 07:09:48 -0700
From: "Paul E. McKenney" <paulmck@...nel.org>
To: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>, linux-kernel@...r.kernel.org,
	Nicholas Piggin <npiggin@...il.com>,
	Michael Ellerman <mpe@...erman.id.au>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	Will Deacon <will@...nel.org>, Boqun Feng <boqun.feng@...il.com>,
	Alan Stern <stern@...land.harvard.edu>,
	John Stultz <jstultz@...gle.com>,
	Neeraj Upadhyay <Neeraj.Upadhyay@....com>,
	Frederic Weisbecker <frederic@...nel.org>,
	Joel Fernandes <joel@...lfernandes.org>,
	Josh Triplett <josh@...htriplett.org>,
	Uladzislau Rezki <urezki@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Lai Jiangshan <jiangshanlai@...il.com>,
	Zqiang <qiang.zhang1211@...il.com>, Ingo Molnar <mingo@...hat.com>,
	Waiman Long <longman@...hat.com>,
	Mark Rutland <mark.rutland@....com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Vlastimil Babka <vbabka@...e.cz>, maged.michael@...il.com,
	Mateusz Guzik <mjguzik@...il.com>,
	Jonas Oberhauser <jonas.oberhauser@...weicloud.com>,
	rcu@...r.kernel.org, linux-mm@...ck.org, lkmm@...ts.linux.dev
Subject: Re: [RFC PATCH 0/4] sched+mm: Track lazy active mm existence with
 hazard pointers

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@...icios.com>
> Cc: Nicholas Piggin <npiggin@...il.com>
> Cc: Michael Ellerman <mpe@...erman.id.au>
> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Cc: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> Cc: "Paul E. McKenney" <paulmck@...nel.org>
> Cc: Will Deacon <will@...nel.org>
> Cc: Boqun Feng <boqun.feng@...il.com>
> Cc: Alan Stern <stern@...land.harvard.edu>
> Cc: John Stultz <jstultz@...gle.com>
> Cc: Neeraj Upadhyay <Neeraj.Upadhyay@....com>
> Cc: Boqun Feng <boqun.feng@...il.com>
> Cc: Frederic Weisbecker <frederic@...nel.org>
> Cc: Joel Fernandes <joel@...lfernandes.org>
> Cc: Josh Triplett <josh@...htriplett.org>
> Cc: Uladzislau Rezki <urezki@...il.com>
> Cc: Steven Rostedt <rostedt@...dmis.org>
> Cc: Lai Jiangshan <jiangshanlai@...il.com>
> Cc: Zqiang <qiang.zhang1211@...il.com>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Waiman Long <longman@...hat.com>
> Cc: Mark Rutland <mark.rutland@....com>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Vlastimil Babka <vbabka@...e.cz>
> Cc: maged.michael@...il.com
> Cc: Mateusz Guzik <mjguzik@...il.com>
> Cc: Jonas Oberhauser <jonas.oberhauser@...weicloud.com>
> Cc: rcu@...r.kernel.org
> Cc: linux-mm@...ck.org
> Cc: lkmm@...ts.linux.dev
> 
> 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