linux-kernel - Re: [PATCH v15 3/6] locking/qspinlock: Introduce CNA into the slow path of qspinlock

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Message-ID: <CAJF2gTQFZEpHK45hd9HXxHxJc4gaCuDQ4wZ2adDzHwGQjA6VFw@mail.gmail.com>
Date:   Thu, 3 Aug 2023 18:28:51 +0800
From:   Guo Ren <guoren@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Alex Kogan <alex.kogan@...cle.com>, linux@...linux.org.uk,
        mingo@...hat.com, will.deacon@....com, arnd@...db.de,
        longman@...hat.com, linux-arch@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        tglx@...utronix.de, bp@...en8.de, hpa@...or.com, x86@...nel.org,
        guohanjun@...wei.com, jglauber@...vell.com,
        steven.sistare@...cle.com, daniel.m.jordan@...cle.com,
        dave.dice@...cle.com
Subject: Re: [PATCH v15 3/6] locking/qspinlock: Introduce CNA into the slow
 path of qspinlock

On Thu, Aug 3, 2023 at 4:50 PM Peter Zijlstra <peterz@...radead.org> wrote:
>
> On Wed, Aug 02, 2023 at 07:14:05PM -0400, Guo Ren wrote:
>
> > The pv_ops is belongs to x86 custom frame work, and it prevent other
> > architectures connect to the CNA spinlock.
>
> static_call() exists as a arch neutral variant of this.
Emm... we have used static_call() in the riscv queued_spin_lock_:
https://lore.kernel.org/all/20230802164701.192791-20-guoren@kernel.org/

But we met a compile problem:

  GEN     .vmlinux.objs
  MODPOST Module.symvers
ERROR: modpost: "__SCK__pv_queued_spin_unlock" [arch/riscv/kvm/kvm.ko]
undefined!
ERROR: modpost: "__SCK__pv_queued_spin_unlock"
[kernel/locking/locktorture.ko] undefined!
ERROR: modpost: "__SCK__pv_queued_spin_unlock" [mm/z3fold.ko] undefined!
ERROR: modpost: "__SCK__pv_queued_spin_unlock"
[fs/nfs_common/grace.ko] undefined!
ERROR: modpost: "__SCK__pv_queued_spin_unlock" [fs/quota/quota_v1.ko] undefined!
ERROR: modpost: "__SCK__pv_queued_spin_unlock" [fs/quota/quota_v2.ko] undefined!
ERROR: modpost: "__SCK__pv_queued_spin_unlock"
[fs/quota/quota_tree.ko] undefined!
ERROR: modpost: "__SCK__pv_queued_spin_unlock" [fs/fuse/virtiofs.ko] undefined!
ERROR: modpost: "__SCK__pv_queued_spin_unlock" [fs/dlm/dlm.ko] undefined!
ERROR: modpost: "__SCK__pv_queued_spin_unlock" [fs/fscache/fscache.ko]
undefined!
WARNING: modpost: suppressed 839 unresolved symbol warnings because
there were too many)
/home/guoren/source/kernel/linux/scripts/Makefile.modpost:144: recipe
for target 'Module.symvers' failed

Our solution is:
EXPORT_SYMBOL(__SCK__pv_queued_spin_unlock);

What do you think about it?

>
> > I'm working on riscv qspinlock on sg2042 64 cores 2/4 NUMA nodes
> > platforms. Here are the patches about riscv CNA qspinlock:
> > https://lore.kernel.org/linux-riscv/20230802164701.192791-19-guoren@kernel.org/
> >
> > What's the next plan for this patch series? I think the two-queue design
> > has satisfied most platforms with two NUMA nodes.
>
> What has been your reason for working on CNA? What lock has been so
> contended you need this?
I wrote the reason here:
https://lore.kernel.org/all/20230802164701.192791-1-guoren@kernel.org/

The target platform is: https://www.sophon.ai/

The two NUMA nodes platform has come out, so we want to measure the
benefit of CNA qspinlock.

Any feedbacks are welcome :)

-- 
Best Regards
 Guo Ren