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

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Message-ID: <d412fa7e-6348-4e51-89e8-4c740184cb2f@efficios.com>
Date: Wed, 2 Oct 2024 11:26:27 -0400
From: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To: paulmck@...nel.org
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 2024-10-02 16:09, Paul E. McKenney wrote:
> 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?

Sure, but they are far less exciting ;-)

nr threads (-t)     speedup
      1                -0.2%
      2                +0.4%
      3                +0.2%
      6                +0.6%
     12                +0.8%
     24                +3%
     48               +12%
     96               +21%
    192               +28%
    384                +4%
    768                -0.6%

Thanks,

Mathieu

> 
> 							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

-- 
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com