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Message-ID: <d788c6aa-c8b9-41b8-b4fb-ac126a4f053f@efficios.com>
Date: Wed, 2 Oct 2024 11:36:09 -0400
From: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To: Matthew Wilcox <willy@...radead.org>, Jens Axboe <axboe@...nel.dk>
Cc: paulmck@...nel.org, 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 17:33, Matthew Wilcox wrote:
> On Wed, Oct 02, 2024 at 11:26:27AM -0400, Mathieu Desnoyers wrote:
>> 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 ;-)
>
> How many CPUs in the system under test?
2 sockets, 96-core per socket:
CPU(s): 384
On-line CPU(s) list: 0-383
Vendor ID: AuthenticAMD
Model name: AMD EPYC 9654 96-Core Processor
CPU family: 25
Model: 17
Thread(s) per core: 2
Core(s) per socket: 96
Socket(s): 2
Stepping: 1
Frequency boost: enabled
CPU(s) scaling MHz: 68%
CPU max MHz: 3709.0000
CPU min MHz: 400.0000
BogoMIPS: 4800.00
Note that Jens Axboe got even more impressive speedups testing this
on his 512-hw-thread EPYC [1] (390% speedup for 192 threads). I've
noticed I had schedstats and sched debug enabled in my config, so I'll
have to re-run my tests.
Thanks,
Mathieu
[1] https://discuss.systems/@axboe@fosstodon.org/113238297041686326
>
>> 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
>>
>>
--
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com
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