From: Thomas Monjalon <thomas@monjalon.net>
To: honnappa.nagarahalli@arm.com, ruifeng.wang@arm.com,
Phil Yang <phil.yang@arm.com>
Cc: dev@dpdk.org, bruce.richardson@intel.com,
konstantin.ananyev@intel.com, dev@dpdk.org,
david.marchand@redhat.com,
David Christensen <drc@linux.vnet.ibm.com>
Subject: Re: [dpdk-dev] atomic operations
Date: Sun, 04 Jul 2021 02:37:44 +0200 [thread overview]
Message-ID: <1806192.QIeOlYoxj9@thomas> (raw)
In-Reply-To: <1879045.6WiRxTbeAL@thomas>
03/07/2021 13:29, Thomas Monjalon:
> In the deprecation notices of DPDK 21.05, we can still read this:
> "
> * rte_atomicNN_xxx: These APIs do not take memory order parameter. This does
> not allow for writing optimized code for all the CPU architectures supported
> in DPDK. DPDK will adopt C11 atomic operations semantics and provide wrappers
> using C11 atomic built-ins. These wrappers must be used for patches that
> need to be merged in 20.08 onwards. This change will not introduce any
> performance degradation.
>
> * rte_smp_*mb: These APIs provide full barrier functionality. However, many
> use cases do not require full barriers. To support such use cases, DPDK will
> adopt C11 barrier semantics and provide wrappers using C11 atomic built-ins.
> These wrappers must be used for patches that need to be merged in 20.08
> onwards. This change will not introduce any performance degradation.
> "
The only new wrapper is rte_atomic_thread_fence(). What else?
We are missing clear recommendations.
> Should we keep these notifications forever?
>
> It is very difficult to find which wrapper to use.
We should make function names explicit instead of "These".
> This is the guide we have:
> https://doc.dpdk.org/guides/prog_guide/writing_efficient_code.html#locks-and-atomic-operations
> There are 2 blog posts:
> https://www.dpdk.org/blog/2021/03/26/dpdk-adopts-the-c11-memory-model/
> https://www.dpdk.org/blog/2021/06/09/reader-writer-concurrency/
>
> Basically it says we should use "__atomic builtins" but there is example
> for simple situations like counters, memory barriers, etc.
Precision: I meant "there is *no* example".
> Please who could work on improving the documentation?
One simple example: increment a counter atomically.
__atomic_fetch_add(&counter, 1, __ATOMIC_RELAXED);
or
__atomic_add_fetch(&counter, 1, __ATOMIC_RELAXED);
next prev parent reply other threads:[~2021-07-04 0:37 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-03 11:29 Thomas Monjalon
2021-07-03 17:30 ` Stephen Hemminger
2021-07-04 0:40 ` Thomas Monjalon
2021-07-04 0:37 ` Thomas Monjalon [this message]
2021-07-05 7:00 ` Ruifeng Wang
2021-07-05 7:30 ` Thomas Monjalon
2021-07-05 8:33 ` Ruifeng Wang
2021-07-05 16:20 ` Stephen Hemminger
2021-07-07 19:04 ` Honnappa Nagarahalli
2021-07-07 19:28 ` Thomas Monjalon
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