[PATCH] kref: prefer atomic_inc_not_zero to atomic_add_unless

[PATCH] kref: prefer atomic_inc_not_zero to atomic_add_unless

[Jason A. Donenfeld]

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] http://open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2167.pdf

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.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_ */
-- 
2.6.0

Re: [PATCH] kref: prefer atomic_inc_not_zero to atomic_add_unless

[Thomas Hellstrom]

Reviewed-by: Thomas Hellstrom <thellstrom@vmware.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@zx2c4.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_ */

Re: [PATCH] kref: prefer atomic_inc_not_zero to atomic_add_unless

[Jason A. Donenfeld]

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@vmware.com> wrote:
> Reviewed-by: Thomas Hellstrom <thellstrom@vmware.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@zx2c4.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_ */
>

Re: [PATCH] kref: prefer atomic_inc_not_zero to atomic_add_unless

[Jason A. Donenfeld]

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@zx2c4.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@vmware.com> wrote:
>> Reviewed-by: Thomas Hellstrom <thellstrom@vmware.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@zx2c4.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_ */
>>

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

[Thomas Hellstrom]

Dave,

Since kref_get_unless_zero() was brought in by drm, could we add this to
drm-next?

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@zx2c4.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@vmware.com> wrote:
>>> Reviewed-by: Thomas Hellstrom <thellstrom@vmware.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@zx2c4.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_ */

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

[Daniel Vetter]

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@zx2c4.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@vmware.com> wrote:
> >>> Reviewed-by: Thomas Hellstrom <thellstrom@vmware.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@zx2c4.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_ */
> 
> 
> _______________________________________________
> dri-devel mailing list
> dri-devel@lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/dri-devel

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

[PATCH] kref: prefer atomic_inc_not_zero to atomic_add_unless

[Jason A. Donenfeld]

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] http://open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2167.pdf

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Reviewed-by: Thomas Hellstrom <thellstrom@vmware.com>
---
This was reviewed favorably 14 months ago but never picked up.
I'm resubmitting it now in hopes that you can finally queue it
up for 4.10.

 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 e15828fd71f1..62f0a84ae94e 100644
--- a/include/linux/kref.h
+++ b/include/linux/kref.h
@@ -133,6 +133,6 @@ 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_ */
-- 
2.11.0

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

[Jason A. Donenfeld]

On Tue, Jul 12, 2016 at 2:28 PM, Daniel Vetter <daniel@ffwll.ch> wrote:
> Sure can do, but I can't find the raw patch anywhere (I suck, I know).
> Care to resend?

Hey sorry I missed this email requesting the actual patch. I reposted it here:

https://lkml.org/lkml/2016/12/14/814

Re: [PATCH] kref: prefer atomic_inc_not_zero to atomic_add_unless

[Christoph Hellwig]

It's also way easier to read using atomic_inc_not_zero..

Reviewed-by: Christoph Hellwig <hch@lst.de>

Not sure you're sending this to the right maintainers, though.  You
probably want to include Greg.