From: Ruifeng Wang <Ruifeng.Wang@arm.com>
To: "Mattias Rönnblom" <hofors@lysator.liu.se>,
"thomas@monjalon.net" <thomas@monjalon.net>,
"david.marchand@redhat.com" <david.marchand@redhat.com>
Cc: "dev@dpdk.org" <dev@dpdk.org>,
"konstantin.v.ananyev@yandex.ru" <konstantin.v.ananyev@yandex.ru>,
Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>,
nd <nd@arm.com>, nd <nd@arm.com>
Subject: RE: [PATCH] eal: add notes to SMP memory barrier APIs
Date: Sun, 25 Jun 2023 08:17:14 +0000 [thread overview]
Message-ID: <AS8PR08MB7080699A237F9351E706AAB29E21A@AS8PR08MB7080.eurprd08.prod.outlook.com> (raw)
In-Reply-To: <4954a01e-53e3-c070-d737-a60c0042c736@lysator.liu.se>
> -----Original Message-----
> From: Mattias Rönnblom <hofors@lysator.liu.se>
> Sent: Friday, June 23, 2023 2:20 AM
> To: Ruifeng Wang <Ruifeng.Wang@arm.com>; thomas@monjalon.net; david.marchand@redhat.com
> Cc: dev@dpdk.org; konstantin.v.ananyev@yandex.ru; Honnappa Nagarahalli
> <Honnappa.Nagarahalli@arm.com>; nd <nd@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.wang@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);
> > ///@}
next prev parent reply other threads:[~2023-06-25 8:17 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-06-21 6:44 Ruifeng Wang
2023-06-21 7:29 ` Thomas Monjalon
2023-06-25 7:55 ` Ruifeng Wang
2023-06-22 18:19 ` Mattias Rönnblom
2023-06-23 21:51 ` Tyler Retzlaff
2023-06-25 8:45 ` Ruifeng Wang
2023-06-25 15:40 ` Thomas Monjalon
2023-06-25 8:17 ` Ruifeng Wang [this message]
2023-06-29 19:28 ` Mattias Rönnblom
2023-07-03 6:12 ` Ruifeng Wang
2023-06-26 7:12 ` [PATCH v2] " Ruifeng Wang
2023-06-29 19:43 ` Mattias Rönnblom
2023-07-03 7:02 ` Ruifeng Wang
2023-07-04 12:08 ` Mattias Rönnblom
2023-07-03 9:56 ` [PATCH v3] " Ruifeng Wang
2023-07-28 9:17 ` Thomas Monjalon
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