[dpdk-dev] [PATCH v1] doc: update atomic operation deprecation

[dpdk-dev] [PATCH v1] doc: update atomic operation deprecation

[Joyce Kong]

Update the incorrect description about atomic operations
with provided wrappers in deprecation doc[1].

[1]https://mails.dpdk.org/archives/dev/2021-July/213333.html

Fixes: 7518c5c4ae6a ("doc: announce adoption of C11 atomic operations semantics")
Cc: stable@dpdk.org

Signed-off-by: Joyce Kong <joyce.kong@arm.com>
Reviewed-by: Ruifeng Wang <ruifeng.wang@arm.com>
---
 doc/guides/rel_notes/deprecation.rst | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/doc/guides/rel_notes/deprecation.rst b/doc/guides/rel_notes/deprecation.rst
index 9584d6bfd7..4142315842 100644
--- a/doc/guides/rel_notes/deprecation.rst
+++ b/doc/guides/rel_notes/deprecation.rst
@@ -19,16 +19,16 @@ Deprecation Notices
 
 * rte_atomicNN_xxx: These APIs do not take memory order parameter. This does
   not allow for writing optimized code for all the CPU architectures supported
-  in DPDK. DPDK will adopt C11 atomic operations semantics and provide wrappers
-  using C11 atomic built-ins. These wrappers must be used for patches that
-  need to be merged in 20.08 onwards. This change will not introduce any
-  performance degradation.
+  in DPDK. DPDK has adopted atomic operations semantics. GCC atomic built-ins
+  must be used for patches that need to be merged in 20.08 onwards. This change
+  will not introduce any performance degradation.
 
 * rte_smp_*mb: These APIs provide full barrier functionality. However, many
-  use cases do not require full barriers. To support such use cases, DPDK will
-  adopt C11 barrier semantics and provide wrappers using C11 atomic built-ins.
-  These wrappers must be used for patches that need to be merged in 20.08
-  onwards. This change will not introduce any performance degradation.
+  use cases do not require full barriers. To support such use cases, DPDK has
+  adopted atomic barrier semantics. GCC atomic built-ins and a new wrapper
+  ``rte_atomic_thread_fence`` instead of ``__atomic_thread_fence`` must be
+  used for patches that need to be merged in 20.08 onwards. This change will
+  not introduce any performance degradation.
 
 * lib: will fix extending some enum/define breaking the ABI. There are multiple
   samples in DPDK that enum/define terminated with a ``.*MAX.*`` value which is
-- 
2.17.1

Re: [dpdk-dev] [PATCH v1] doc: update atomic operation deprecation

[Honnappa Nagarahalli]

<snip>

> 
> Update the incorrect description about atomic operations with provided
> wrappers in deprecation doc[1].
> 
> [1]https://mails.dpdk.org/archives/dev/2021-July/213333.html
> 
> Fixes: 7518c5c4ae6a ("doc: announce adoption of C11 atomic operations
> semantics")
> Cc: stable@dpdk.org
> 
> Signed-off-by: Joyce Kong <joyce.kong@arm.com>
> Reviewed-by: Ruifeng Wang <ruifeng.wang@arm.com>
> ---
>  doc/guides/rel_notes/deprecation.rst | 16 ++++++++--------
>  1 file changed, 8 insertions(+), 8 deletions(-)
> 
> diff --git a/doc/guides/rel_notes/deprecation.rst
> b/doc/guides/rel_notes/deprecation.rst
> index 9584d6bfd7..4142315842 100644
> --- a/doc/guides/rel_notes/deprecation.rst
> +++ b/doc/guides/rel_notes/deprecation.rst
> @@ -19,16 +19,16 @@ Deprecation Notices
> 
>  * rte_atomicNN_xxx: These APIs do not take memory order parameter. This
> does
>    not allow for writing optimized code for all the CPU architectures supported
> -  in DPDK. DPDK will adopt C11 atomic operations semantics and provide
> wrappers
> -  using C11 atomic built-ins. These wrappers must be used for patches that
> -  need to be merged in 20.08 onwards. This change will not introduce any
> -  performance degradation.
> +  in DPDK. DPDK has adopted atomic operations semantics. GCC atomic
> + built-ins  must be used for patches that need to be merged in 20.08
> + onwards. This change  will not introduce any performance degradation.
Since there have been objections to the language used to refer to GCC C11 atomic built-ins, may be we add a reference to the GCC pages?

DPDK has adopted the atomic operations from https://gcc.gnu.org/onlinedocs/gcc/_005f_005fatomic-Builtins.html. These operations must be used for patches that need to be merged in 20.08 onwards. This change  will not introduce any performance degradation.

> 
>  * rte_smp_*mb: These APIs provide full barrier functionality. However, many
> -  use cases do not require full barriers. To support such use cases, DPDK will
> -  adopt C11 barrier semantics and provide wrappers using C11 atomic built-
> ins.
> -  These wrappers must be used for patches that need to be merged in 20.08
> -  onwards. This change will not introduce any performance degradation.
> +  use cases do not require full barriers. To support such use cases,
> + DPDK has  adopted atomic barrier semantics. GCC atomic built-ins and a
> + new wrapper  ``rte_atomic_thread_fence`` instead of
> + ``__atomic_thread_fence`` must be  used for patches that need to be
> + merged in 20.08 onwards. This change will  not introduce any performance
> degradation.
Same here.
To support such use cases, DPDK has  adopted atomic operations from https://gcc.gnu.org/onlinedocs/gcc/_005f_005fatomic-Builtins.html. A new wrapper  ``rte_atomic_thread_fence`` instead of ``__atomic_thread_fence`` must be  used for patches that need to be merged in 20.08 onwards. This change will  not introduce any performance degradation.

> 
>  * lib: will fix extending some enum/define breaking the ABI. There are
> multiple
>    samples in DPDK that enum/define terminated with a ``.*MAX.*`` value
> which is
> --
> 2.17.1

[dpdk-dev] [PATCH v2] doc: update atomic operation deprecation

[Joyce Kong]

Update the incorrect description about atomic operations
with provided wrappers in deprecation doc[1].

[1]https://mails.dpdk.org/archives/dev/2021-July/213333.html

Fixes: 7518c5c4ae6a ("doc: announce adoption of C11 atomic operations semantics")
Cc: stable@dpdk.org

Signed-off-by: Joyce Kong <joyce.kong@arm.com>
Reviewed-by: Ruifeng Wang <ruifeng.wang@arm.com>
---
 doc/guides/rel_notes/deprecation.rst | 18 ++++++++++--------
 1 file changed, 10 insertions(+), 8 deletions(-)

diff --git a/doc/guides/rel_notes/deprecation.rst b/doc/guides/rel_notes/deprecation.rst
index 9584d6bfd7..a4f350fa09 100644
--- a/doc/guides/rel_notes/deprecation.rst
+++ b/doc/guides/rel_notes/deprecation.rst
@@ -19,16 +19,18 @@ Deprecation Notices
 
 * rte_atomicNN_xxx: These APIs do not take memory order parameter. This does
   not allow for writing optimized code for all the CPU architectures supported
-  in DPDK. DPDK will adopt C11 atomic operations semantics and provide wrappers
-  using C11 atomic built-ins. These wrappers must be used for patches that
-  need to be merged in 20.08 onwards. This change will not introduce any
-  performance degradation.
+  in DPDK. DPDK has adopted the atomic operations from
+  https://gcc.gnu.org/onlinedocs/gcc/_005f_005fatomic-Builtins.html. These
+  operations must be used for patches that need to be merged in 20.08 onwards.
+  This change will not introduce any performance degradation.
 
 * rte_smp_*mb: These APIs provide full barrier functionality. However, many
-  use cases do not require full barriers. To support such use cases, DPDK will
-  adopt C11 barrier semantics and provide wrappers using C11 atomic built-ins.
-  These wrappers must be used for patches that need to be merged in 20.08
-  onwards. This change will not introduce any performance degradation.
+  use cases do not require full barriers. To support such use cases, DPDK has
+  adopted atomic operations from
+  https://gcc.gnu.org/onlinedocs/gcc/_005f_005fatomic-Builtins.html. These
+  operations and a new wrapper ``rte_atomic_thread_fence`` instead of
+  ``__atomic_thread_fence`` must be used for patches that need to be merged in
+  20.08 onwards. This change will not introduce any performance degradation.
 
 * lib: will fix extending some enum/define breaking the ABI. There are multiple
   samples in DPDK that enum/define terminated with a ``.*MAX.*`` value which is
-- 
2.17.1

Re: [dpdk-dev] [PATCH v2] doc: update atomic operation deprecation

[Thomas Monjalon]

23/07/2021 11:49, Joyce Kong:
> Update the incorrect description about atomic operations
> with provided wrappers in deprecation doc[1].
> 
> [1]https://mails.dpdk.org/archives/dev/2021-July/213333.html
> 
> Fixes: 7518c5c4ae6a ("doc: announce adoption of C11 atomic operations semantics")
> Cc: stable@dpdk.org
> 
> Signed-off-by: Joyce Kong <joyce.kong@arm.com>
> Reviewed-by: Ruifeng Wang <ruifeng.wang@arm.com>

Applied, thanks.

Considering all the questions regarding usage of atomics,
I still think we need a documentation about their correct use.

Re: [dpdk-dev] [PATCH v2] doc: update atomic operation deprecation

[Honnappa Nagarahalli]

> -----Original Message-----
> From: Thomas Monjalon <thomas@monjalon.net>
> Sent: Saturday, July 31, 2021 3:27 PM
> To: Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>; Ruifeng Wang
> <Ruifeng.Wang@arm.com>; Joyce Kong <Joyce.Kong@arm.com>
> Cc: stephen@networkplumber.org; mdr@ashroe.eu; dev@dpdk.org; nd
> <nd@arm.com>; stable@dpdk.org
> Subject: Re: [dpdk-dev] [PATCH v2] doc: update atomic operation deprecation
> 
> 23/07/2021 11:49, Joyce Kong:
> > Update the incorrect description about atomic operations with provided
> > wrappers in deprecation doc[1].
> >
> > [1]https://mails.dpdk.org/archives/dev/2021-July/213333.html
> >
> > Fixes: 7518c5c4ae6a ("doc: announce adoption of C11 atomic operations
> > semantics")
> > Cc: stable@dpdk.org
> >
> > Signed-off-by: Joyce Kong <joyce.kong@arm.com>
> > Reviewed-by: Ruifeng Wang <ruifeng.wang@arm.com>
> 
> Applied, thanks.
> 
> Considering all the questions regarding usage of atomics, I still think we need a
> documentation about their correct use.
I think few things to document are:
1) Use of __atomic_add_fetch vs __atomic_fetch_add
2) Using __ATOMIC_RELAXED for statistics
3) Using rte_atomic_thread_fence API

Anything else?


> 

Re: [dpdk-dev] [PATCH v2] doc: update atomic operation deprecation

[Thomas Monjalon]

02/08/2021 19:22, Honnappa Nagarahalli:
> From: Thomas Monjalon <thomas@monjalon.net>
> > 23/07/2021 11:49, Joyce Kong:
> > Considering all the questions regarding usage of atomics, I still think we need a
> > documentation about their correct use.
> 
> I think few things to document are:
> 1) Use of __atomic_add_fetch vs __atomic_fetch_add
> 2) Using __ATOMIC_RELAXED for statistics
> 3) Using rte_atomic_thread_fence API

That's a good list.
Let's start with that please.

I would like an explanation about when full barrier may be used.