> -----Original Message----- > From: Mattias Rönnblom <hof...@lysator.liu.se> > Sent: Friday, June 30, 2023 3:44 AM > To: Ruifeng Wang <ruifeng.w...@arm.com>; tho...@monjalon.net; > david.march...@redhat.com > Cc: dev@dpdk.org; roret...@linux.microsoft.com; > konstantin.v.anan...@yandex.ru; Honnappa > Nagarahalli <honnappa.nagaraha...@arm.com>; nd <n...@arm.com> > Subject: Re: [PATCH v2] eal: add notes to SMP memory barrier APIs > > On 2023-06-26 09:12, 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> > > --- > > v2: Made the notes more specific. > > > > lib/eal/include/generic/rte_atomic.h | 19 +++++++++++++++++++ > > 1 file changed, 19 insertions(+) > > > > diff --git a/lib/eal/include/generic/rte_atomic.h > > b/lib/eal/include/generic/rte_atomic.h > > index 58df843c54..35e0041ce6 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 provides fence synchronization > > + * primitive but doesn't take memory order parameter. > > + * rte_atomic_thread_fence() should be used instead. > > I can't see why coding the memory model semantics into the name, rather than > by > specification-by-means-of-a-parameter, could be the real issue. > Could you explain? Seems like just different syntax to me.
Yes, rte_smp_xx and rte_atomic_thread_fence have different syntaxes. The compiler atomic builtins were accepted for memory ordering. It comprises atomic arithmetic, atomic load/store, and atomic fence. It is simpler and clearer to do memory ordering by using the atomic builtins whenever possible. rte_smp_xx has functionality overlap with atomic fence builtins but with different memory model semantics and different syntaxes. Because of the differences, it will make memory ordering a little more complex if rte_smp_xx is kept aside atomic builtins suite. > > The old <rte_atomic.h> atomic arithmetic and atomic load/store operations > suffered from > unspecified semantics in regards to any ordering they imposed on other memory > accesses. I > guess that shortcoming could be described as a "missing parameter", although > that too > would be misleading. Unclear semantics seems not be the case for the > kernel-style barriers > though. > > > */ > > 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 provides fence synchronization > > + * primitive but doesn't take memory order parameter. > > + * 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 provides fence synchronization > > + * primitive but doesn't take memory order parameter. > > + * rte_atomic_thread_fence() should be used instead. > > */ > > static inline void rte_smp_rmb(void); > > ///@} > > @@ -122,6 +137,10 @@ static inline void rte_io_rmb(void); > > > > /** > > * Synchronization fence between threads based on the specified memory > > order. > > + * > > + * @param memorder > > + * The memory order defined by compiler atomic builtin at: > > + * https://gcc.gnu.org/onlinedocs/gcc/_005f_005fatomic-Builtins.html > > */ > > static inline void rte_atomic_thread_fence(int memorder); > >
