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

[Matthew Wilcox]

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?

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