> -----Original Message----- > From: Mattias Rönnblom <hof...@lysator.liu.se> > Sent: Friday, June 30, 2023 3:28 AM > To: Ruifeng Wang <ruifeng.w...@arm.com>; tho...@monjalon.net; > david.march...@redhat.com > Cc: dev@dpdk.org; konstantin.v.anan...@yandex.ru; Honnappa Nagarahalli > <honnappa.nagaraha...@arm.com>; nd <n...@arm.com> > Subject: Re: [PATCH] eal: add notes to SMP memory barrier APIs > > On 2023-06-25 10:17, Ruifeng Wang wrote: > >> -----Original Message----- > >> From: Mattias Rönnblom <hof...@lysator.liu.se> > >> Sent: Friday, June 23, 2023 2:20 AM > >> To: Ruifeng Wang <ruifeng.w...@arm.com>; tho...@monjalon.net; > >> david.march...@redhat.com > >> Cc: dev@dpdk.org; konstantin.v.anan...@yandex.ru; Honnappa > >> Nagarahalli <honnappa.nagaraha...@arm.com>; nd <n...@arm.com> > >> Subject: Re: [PATCH] eal: add notes to SMP memory barrier APIs > >> > >> On 2023-06-21 08:44, Ruifeng Wang wrote: > >>> The rte_smp_xx() APIs are deprecated. But it is not mentioned in the > >>> function header. > >>> Added notes in function header for clarification. > >>> > >>> Signed-off-by: Ruifeng Wang <ruifeng.w...@arm.com> > >>> --- > >>> lib/eal/include/generic/rte_atomic.h | 15 +++++++++++++++ > >>> 1 file changed, 15 insertions(+) > >>> > >>> diff --git a/lib/eal/include/generic/rte_atomic.h > >>> b/lib/eal/include/generic/rte_atomic.h > >>> index 58df843c54..542a2c16ff 100644 > >>> --- a/lib/eal/include/generic/rte_atomic.h > >>> +++ b/lib/eal/include/generic/rte_atomic.h > >>> @@ -55,6 +55,11 @@ static inline void rte_rmb(void); > >>> * Guarantees that the LOAD and STORE operations that precede the > >>> * rte_smp_mb() call are globally visible across the lcores > >>> * before the LOAD and STORE operations that follows it. > >>> + * > >>> + * @note > >>> + * This function is deprecated. It adds complexity to the memory > >>> + model > >>> + * used by this project. C11 memory model should always be used. > >>> + * rte_atomic_thread_fence() should be used instead. > >> > >> It's somewhat confusing to learn I should use the C11 memory model, > >> and then in the next sentence that I should call a function which is not > >> in C11. > > > > I should say "memory order semantics". It will be more specific. > > The wrapper function rte_atomic_thread_fence is a special case. It > > provides an optimized implementation for __ATOMIC_SEQ_CST for x86: > > https://www.dpdk.org/blog/2021/03/26/dpdk-adopts-the-c11-memory-model/ > > > >> > >> I think it would be helpful to say which memory_model parameters > >> should be used to replace the rte_smp_*mb() calls, and if there are > >> any difference in semantics between the Linux kernel-style barriers and > >> their C11 > (near-)equivalents. > > > > As compiler atomic built-ins are being used. The memory model parameters > > should be the > ones listed in: > > https://gcc.gnu.org/onlinedocs/gcc/_005f_005fatomic-Builtins.html > > We are not taking Linux kernel-style barriers. So no need to mention that. > > > > Yeah, sure. But which one of the C11 memory models, for respective legacy > barrier? > > What you are moving from is Linux kernel-style barriers, so if you are to > recommend a > migration path, their semantics will matter.
Got it. I can add the suggested memory_model parameters for respective legacy barrier. > > >> > >> Is there some particular reason these functions aren't marked > >> __rte_deprecated? Too many warnings? > > > > Yes, warnings will come up. Some occurrences still remain in the project. > > > >> > >>> */ > >>> static inline void rte_smp_mb(void); > >>> > >>> @@ -64,6 +69,11 @@ static inline void rte_smp_mb(void); > >>> * Guarantees that the STORE operations that precede the > >>> * rte_smp_wmb() call are globally visible across the lcores > >>> * before the STORE operations that follows it. > >>> + * > >>> + * @note > >>> + * This function is deprecated. It adds complexity to the memory > >>> + model > >>> + * used by this project. C11 memory model should always be used. > >>> + * rte_atomic_thread_fence() should be used instead. > >>> */ > >>> static inline void rte_smp_wmb(void); > >>> > >>> @@ -73,6 +83,11 @@ static inline void rte_smp_wmb(void); > >>> * Guarantees that the LOAD operations that precede the > >>> * rte_smp_rmb() call are globally visible across the lcores > >>> * before the LOAD operations that follows it. > >>> + * > >>> + * @note > >>> + * This function is deprecated. It adds complexity to the memory > >>> + model > >>> + * used by this project. C11 memory model should always be used. > >>> + * rte_atomic_thread_fence() should be used instead. > >>> */ > >>> static inline void rte_smp_rmb(void); > >>> ///@}
