linux-kernel - Re: [PATCH] locking/pvqspinlock/x86: Use _Q_LOCKED_VAL in PV_UNLOCK

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Date: Mon, 22 Apr 2024 22:12:11 +0200
From: Uros Bizjak <ubizjak@...il.com>
To: Boqun Feng <boqun.feng@...il.com>
Cc: x86@...nel.org, linux-kernel@...r.kernel.org, 
	Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...nel.org>, Will Deacon <will@...nel.org>, 
	Waiman Long <longman@...hat.com>
Subject: Re: [PATCH] locking/pvqspinlock/x86: Use _Q_LOCKED_VAL in
 PV_UNLOCK_ASM macro

On Mon, Apr 22, 2024 at 10:00 PM Boqun Feng <boqun.feng@...il.com> wrote:
>
> On Mon, Apr 22, 2024 at 09:57:04PM +0200, Uros Bizjak wrote:
> > On Mon, Apr 22, 2024 at 9:45 PM Boqun Feng <boqun.feng@...il.com> wrote:
> >
> > > > diff --git a/arch/x86/include/asm/qspinlock_paravirt.h b/arch/x86/include/asm/qspinlock_paravirt.h
> > > > index 466af57b8ed6..0a985784be9b 100644
> > > > --- a/arch/x86/include/asm/qspinlock_paravirt.h
> > > > +++ b/arch/x86/include/asm/qspinlock_paravirt.h
> > > > @@ -40,7 +40,7 @@ __PV_CALLEE_SAVE_REGS_THUNK(__pv_queued_spin_unlock_slowpath, ".spinlock.text");
> > > >  #define PV_UNLOCK_ASM                                                        \
> > > >       FRAME_BEGIN                                                     \
> > > >       "push  %rdx\n\t"                                                \
> > > > -     "mov   $0x1,%eax\n\t"                                           \
> > > > +     "mov   $" __stringify(_Q_LOCKED_VAL) ",%eax\n\t"                \
> > > >       "xor   %edx,%edx\n\t"                                           \
> > > >       LOCK_PREFIX "cmpxchg %dl,(%rdi)\n\t"                            \
> > > >       "jne   .slowpath\n\t"                                           \
> > >
> > > There is also a "cmp $0x1,%al" afterwards.
> >
> > Not anymore. Please note that the patch is against -tip, where we have:
> >
>
> Oh, thanks for the information. Maybe it makes sense to mention the
> patches dependency in the commit log?

Hm, yes ... I should mention this as "[PATCH -tip]" in the subject
line to avoid confusion with this particular patch.

Thanks,
Uros.