> From: Tyler Retzlaff [mailto:roret...@linux.microsoft.com] > Sent: Wednesday, 1 February 2023 22.41 > > On Wed, Feb 01, 2023 at 01:07:59AM +0000, Honnappa Nagarahalli wrote: > > > > > From: Thomas Monjalon <tho...@monjalon.net> > > > Sent: Tuesday, January 31, 2023 4:42 PM > > > > > > Honnappa, please could you give your view on the future of atomics > in DPDK? > > Thanks Thomas, apologies it has taken me a while to get to this > discussion. > > > > IMO, we do not need DPDK's own abstractions. APIs from stdatomic.h > (stdatomics as is called here) already serve the purpose. These APIs > are well understood and documented. > > i agree that whatever atomics APIs we advocate for should align with > the > standard C atomics for the reasons you state including implied > semantics. > > > > > For environments where stdatomics are not supported, we could have a > stdatomic.h in DPDK implementing the same APIs (we have to support only > _explicit APIs). This allows the code to use stdatomics APIs and when > we move to minimum supported standard C11, we just need to get rid of > the file in DPDK repo.
Perhaps we can use something already existing, such as this: https://android.googlesource.com/platform/bionic/+/lollipop-release/libc/include/stdatomic.h > > my concern with this is that if we provide a stdatomic.h or introduce > names > from stdatomic.h it's a violation of the C standard. > > references: > * ISO/IEC 9899:2011 sections 7.1.2, 7.1.3. > * GNU libc manual > https://www.gnu.org/software/libc/manual/html_node/Reserved- > Names.html > > in effect the header, the names and in some instances namespaces > introduced > are reserved by the implementation. there are several reasons in the > GNU libc > manual that explain the justification for these reservations and if > if we think about ODR and ABI compatibility we can conceive of others. I we are going to move to C11 soon, I consider the shim interim, and am inclined to ignore these warning factors. If we are not moving to C11 soon, I would consider these disadvantages more seriously. > > i'll also remark that the inter-mingling of names from the POSIX > standard implicitly exposed as a part of the EAL public API has been > problematic for portability. This is a very important remark, which should be considered carefully! Tyler has firsthand experience with DPDK portability. If he thinks porting to Windows is going to be a headache if we expose the stdatomic.h API, we must listen! So, what is your gut feeling here, Tyler? > > let's discuss this from here. if there's still overwhelming desire to > go > this route then we'll just do our best. > > ty I have a preference for exposing the stdatomic.h API. Tyler listed the disadvantages above. (I also have a preference for moving to C11 soon.) Exposing a 1:1 similar API with RTE prefixes would also be acceptable for me. The disadvantage is that the names are different than the C11 names, which might lead to some confusion. And from an ABI stability perspective, such an important API should not be marked experimental. This means that years will pass before we can get rid of it again, due to ABI stability policies. -Morten
