Re: [PATCH v4] lib/dlock-list: Scale dlock_lists_empty()

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To: Davidlohr Bueso <dave@xxxxxxxxxxxx>
Subject: Re: [PATCH v4] lib/dlock-list: Scale dlock_lists_empty()
From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Date: Thu, 9 Nov 2017 18:30:27 +0100
Cc: Boqun Feng <boqun.feng@xxxxxxxxx>, Andreas Dilger <adilger@xxxxxxxxx>, Jan Kara <jack@xxxxxxx>, Waiman Long <longman@xxxxxxxxxx>, Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>, Jan Kara <jack@xxxxxxxx>, Jeff Layton <jlayton@xxxxxxxxxxxxxxx>, "J. Bruce Fields" <bfields@xxxxxxxxxxxx>, Tejun Heo <tj@xxxxxxxxxx>, Christoph Lameter <cl@xxxxxxxxxxxxxxxxxxxx>, linux-fsdevel@xxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, Ingo Molnar <mingo@xxxxxxxxxx>, Andi Kleen <andi@xxxxxxxxxxxxxx>, Dave Chinner <dchinner@xxxxxxxxxx>
In-reply-to: <20171109172408.q5oo7u5skc5vjswb@linux-n805>
User-agent: NeoMutt/20170609 (1.8.3)

On Thu, Nov 09, 2017 at 09:24:08AM -0800, Davidlohr Bueso wrote:
> On Wed, 08 Nov 2017, Boqun Feng wrote:
> > Or worse:
> > 
> > 	 * CPU0				    CPU1
> > 	 * dlock_list_add()                 dlock_lists_empty()
> > 	 *					  smp_mb__before_atomic();
> > 	 *				      [L] atomic_read(used_lists)

Note that this is broken; smp_mb__before_atomic() is not valid on
atomic_read().

> > 	 *   [S] atomic_inc(used_lists);
> > 	 *       smp_mb__after_atomic();
> >

References:
- Re: [PATCH v8 1/6] lib/dlock-list: Distributed and lock-protected lists
  - From: Davidlohr Bueso
- Re: [PATCH v8 1/6] lib/dlock-list: Distributed and lock-protected lists
  - From: Waiman Long
- Re: [PATCH v8 1/6] lib/dlock-list: Distributed and lock-protected lists
  - From: Davidlohr Bueso
- [PATCH v3] lib/dlock-list: Scale dlock_lists_empty()
  - From: Davidlohr Bueso
- Re: [PATCH v3] lib/dlock-list: Scale dlock_lists_empty()
  - From: Waiman Long
- [PATCH v4] lib/dlock-list: Scale dlock_lists_empty()
  - From: Davidlohr Bueso
- Re: [PATCH v4] lib/dlock-list: Scale dlock_lists_empty()
  - From: Jan Kara
- Re: [PATCH v4] lib/dlock-list: Scale dlock_lists_empty()
  - From: Andreas Dilger
- Re: [PATCH v4] lib/dlock-list: Scale dlock_lists_empty()
  - From: Boqun Feng
- Re: [PATCH v4] lib/dlock-list: Scale dlock_lists_empty()
  - From: Davidlohr Bueso

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