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[204.195.96.226]) by smtp.gmail.com with ESMTPSA id a92af1059eb24-137eda36ddbsm846494c88.12.2026.06.01.15.07.16 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 01 Jun 2026 15:07:16 -0700 (PDT) Date: Mon, 1 Jun 2026 15:07:10 -0700 From: Stephen Hemminger To: dev@dpdk.org Cc: Konstantin Ananyev , Wathsala Vithanage Subject: Re: [PATCH v4 03/27] ring: unify memory model on C11, remove atomic32 Message-ID: <20260601150710.1f7ad9e9@phoenix.local> In-Reply-To: <20260526232542.620966-4-stephen@networkplumber.org> References: <20260521042043.1590536-1-stephen@networkplumber.org> <20260526232542.620966-1-stephen@networkplumber.org> <20260526232542.620966-4-stephen@networkplumber.org> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-BeenThere: dev@dpdk.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: DPDK patches and discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dev-bounces@dpdk.org On Tue, 26 May 2026 16:23:53 -0700 Stephen Hemminger wrote: > Remove the RTE_USE_C11_MEM_MODEL build switch; C11 atomics are now > the default for all platforms. Unifies __rte_ring_update_tail into > the C11 form (atomic_store_release replaces the older rte_smp_wmb + > plain store on the generic path) and renames rte_ring_generic_pvt.h > to rte_ring_x86_pvt.h to reflect its new scope. > > Also splits the head-move helper into separate ST and MT variants, > removing the runtime is_st branch from the MT retry loop. > This gets small boost and scopes the following exception > more tightly. > > Exception: on x86 with GCC, atomic_compare_exchange on the head CAS > regresses MP/MC contended throughput by ~20% existing hand-written > cmpxchg. As a workaround, GCC-on-x86 builds use the older > __sync_bool_compare_and_swap builtin, which generates equivalent > code to the original asm. Can be reverted if/when GCC gets > fixed; similar issue was observed in Linux kernel. > > Signed-off-by: Stephen Hemminger > --- This is a big enough change, going to split it up as its own series.