linux-kernel - Re: Patch for drm-next WAS Re: [PATCH] kref: prefer atomic_inc_not_zero to atomic_add_unless

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Date:	Tue, 12 Jul 2016 14:28:17 +0200
From:	Daniel Vetter <daniel@...ll.ch>
To:	Thomas Hellstrom <thellstrom@...are.com>
Cc:	Dave Airlie <airlied@...hat.com>,
	"Jason A. Donenfeld" <Jason@...c4.com>,
	Paul McKenney <paulmck@...ux.vnet.ibm.com>,
	LKML <linux-kernel@...r.kernel.org>,
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>
Subject: Re: Patch for drm-next WAS Re: [PATCH] kref: prefer
 atomic_inc_not_zero to atomic_add_unless

On Fri, Jul 01, 2016 at 09:08:34AM +0200, Thomas Hellstrom wrote:
> Dave,
> 
> Since kref_get_unless_zero() was brought in by drm, could we add this to
> drm-next?

Sure can do, but I can't find the raw patch anywhere (I suck, I know).
Care to resend?

Thanks, Daniel

> 
> Thanks,
> Thomas
> 
> 
> On 06/30/2016 12:52 AM, Jason A. Donenfeld wrote:
> > This was positively reviewed by maintainers but never picked up. Can
> > someone queue this for 4.7 or 4.8?
> >
> > Thanks,
> > Jason
> >
> > On Mon, Feb 1, 2016 at 10:53 PM, Jason A. Donenfeld <Jason@...c4.com> wrote:
> >> This was positively reviewed but never picked up. Can someone queue
> >> this for rc3?
> >>
> >> Thanks,
> >> Jason
> >>
> >> On Sun, Oct 11, 2015 at 9:59 PM, Thomas Hellstrom <thellstrom@...are.com> wrote:
> >>> Reviewed-by: Thomas Hellstrom <thellstrom@...are.com>
> >>>
> >>>
> >>> On 10/10/2015 12:56 PM, Jason A. Donenfeld wrote:
> >>>> On most platforms, there exists this ifdef:
> >>>>
> >>>>  #define atomic_inc_not_zero(v) atomic_add_unless((v), 1, 0)
> >>>>
> >>>> This makes this patch functionally useless. However, on PPC, there is
> >>>> actually an explicit definition of atomic_inc_not_zero with its own
> >>>> assembly that is slightly more optimized than atomic_add_unless. So,
> >>>> this patch changes kref to use atomic_inc_not_zero instead, for PPC and
> >>>> any future platforms that might provide an explicit implementation.
> >>>>
> >>>> This also puts this usage of kref more in line with a verbatim reading
> >>>> of the examples in Paul McKenney's paper [1] in the section titled "2.4
> >>>> Atomic Counting With Check and Release Memory Barrier", which uses
> >>>> atomic_inc_not_zero.
> >>>>
> >>>> [1] https://urldefense.proofpoint.com/v2/url?u=http-3A__open-2Dstd.org_jtc1_sc22_wg21_docs_papers_2007_n2167.pdf&d=BQIBAg&c=Sqcl0Ez6M0X8aeM67LKIiDJAXVeAw-YihVMNtXt-uEs&r=vpukPkBtpoNQp2IUKuFviOmPNYWVKmen3Jeeu55zmEA&m=z5Nd9sYiJMKiphNjyZp6XT5CbayXMBlcb903f260pDY&s=HEHX3CuXRs2GRRQWuC4Vef6iJMwdilKVRkiZgJpjEpA&e=
> >>>>
> >>>> Signed-off-by: Jason A. Donenfeld <Jason@...c4.com>
> >>>> ---
> >>>>  include/linux/kref.h | 2 +-
> >>>>  1 file changed, 1 insertion(+), 1 deletion(-)
> >>>>
> >>>> diff --git a/include/linux/kref.h b/include/linux/kref.h
> >>>> index 484604d..83d1f94 100644
> >>>> --- a/include/linux/kref.h
> >>>> +++ b/include/linux/kref.h
> >>>> @@ -166,6 +166,6 @@ static inline int kref_put_mutex(struct kref *kref,
> >>>>   */
> >>>>  static inline int __must_check kref_get_unless_zero(struct kref *kref)
> >>>>  {
> >>>> -     return atomic_add_unless(&kref->refcount, 1, 0);
> >>>> +     return atomic_inc_not_zero(&kref->refcount);
> >>>>  }
> >>>>  #endif /* _KREF_H_ */
> 
> 
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> dri-devel@...ts.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/dri-devel

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch

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