> -----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. > > 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); > > ///@}
