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[2003:cb:c704:3500:b8a3:191c:eae:cc05]) by smtp.gmail.com with ESMTPSA id n8-20020a05600c304800b003e21f01c426sm10130353wmh.9.2023.03.06.05.32.31 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 06 Mar 2023 05:32:31 -0800 (PST) Message-ID: Date: Mon, 6 Mar 2023 14:32:31 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.8.0 Subject: Re: [PATCH 6/8] aio-wait: switch to smp_mb__after_rmw() Content-Language: en-US To: Paolo Bonzini , qemu-devel@nongnu.org Cc: gshan@redhat.com, eesposit@redhat.com, stefanha@redhat.com, cohuck@redhat.com, eauger@redhat.com References: <20230303171939.237819-1-pbonzini@redhat.com> <20230303171939.237819-7-pbonzini@redhat.com> From: David Hildenbrand Organization: Red Hat In-Reply-To: <20230303171939.237819-7-pbonzini@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=170.10.133.124; envelope-from=david@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On 03.03.23 18:19, Paolo Bonzini wrote: > The barrier comes after an atomic increment, so it is enough to use > smp_mb__after_rmw(); this avoids a double barrier on x86 systems. > > Signed-off-by: Paolo Bonzini > --- > include/block/aio-wait.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/include/block/aio-wait.h b/include/block/aio-wait.h > index dd9a7f6461ef..da13357bb8cf 100644 > --- a/include/block/aio-wait.h > +++ b/include/block/aio-wait.h > @@ -85,7 +85,7 @@ extern AioWait global_aio_wait; > /* Increment wait_->num_waiters before evaluating cond. */ \ > qatomic_inc(&wait_->num_waiters); \ > /* Paired with smp_mb in aio_wait_kick(). */ \ > - smp_mb(); \ > + smp_mb__after_rmw(); \ > if (ctx_ && in_aio_context_home_thread(ctx_)) { \ > while ((cond)) { \ > aio_poll(ctx_, true); \ Reviewed-by: David Hildenbrand -- Thanks, David / dhildenb