Re: [PATCH v3 05/14] locking/qspinlock: Remove unbounded cmpxchg loop from locking slowpath

[Will Deacon]

Hi Waiman,

On Thu, Apr 26, 2018 at 04:16:30PM -0400, Waiman Long wrote:
> On 04/26/2018 06:34 AM, Will Deacon wrote:
> > diff --git a/kernel/locking/qspinlock_paravirt.h b/kernel/locking/qspinlock_paravirt.h
> > index 2711940429f5..2dbad2f25480 100644
> > --- a/kernel/locking/qspinlock_paravirt.h
> > +++ b/kernel/locking/qspinlock_paravirt.h
> > @@ -118,11 +118,6 @@ static __always_inline void set_pending(struct qspinlock *lock)
> >  	WRITE_ONCE(lock->pending, 1);
> >  }
> >  
> > -static __always_inline void clear_pending(struct qspinlock *lock)
> > -{
> > -	WRITE_ONCE(lock->pending, 0);
> > -}
> > -
> >  /*
> >   * The pending bit check in pv_queued_spin_steal_lock() isn't a memory
> >   * barrier. Therefore, an atomic cmpxchg_acquire() is used to acquire the
> 
> There is another clear_pending() function after the "#else /*
> _Q_PENDING_BITS == 8 */" line that need to be removed as well.

Bugger, sorry I missed that one. Is the >= 16K CPUs case supported elsewhere
in Linux? The x86 Kconfig appears to clamp NR_CPUS to 8192 iiuc.

Anyway, additional patch below. Ingo -- please can you apply this on top?

Thanks,

Will

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