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

[Mathieu Desnoyers]

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@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