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Mon, 06 Mar 2023 14:33:26 -0800 (PST) X-Google-Smtp-Source: AK7set+zLAL5/HeUHoEfMnyEVOtw0KnQh2C5cx80Vnpz55rNIky7NzLRHfJ1hwbZnjpZBhvX3ki0xw== X-Received: by 2002:a17:907:9702:b0:8b2:d30:e722 with SMTP id jg2-20020a170907970200b008b20d30e722mr15987757ejc.3.1678142005742; Mon, 06 Mar 2023 14:33:25 -0800 (PST) From: Paolo Bonzini To: qemu-devel@nongnu.org Cc: gshan@redhat.com, eesposit@redhat.com, david@redhat.com, stefanha@redhat.com, cohuck@redhat.com, eauger@redhat.com, richard.henderson@linaro.org Subject: [PATCH v2 5/9] aio-wait: switch to smp_mb__after_rmw() Date: Mon, 6 Mar 2023 23:33:02 +0100 Message-Id: <20230306223306.84383-6-pbonzini@redhat.com> X-Mailer: git-send-email 2.39.1 In-Reply-To: <20230306223306.84383-1-pbonzini@redhat.com> References: <20230306223306.84383-1-pbonzini@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Received-SPF: pass client-ip=170.10.133.124; envelope-from=pbonzini@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, 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+importer=patchew.org@nongnu.org Sender: qemu-devel-bounces+importer=patchew.org@nongnu.org X-ZohoMail-DKIM: pass (identity @redhat.com) X-ZM-MESSAGEID: 1678142040328100007 Content-Type: text/plain; charset="utf-8" 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. Reviewed-by: Richard Henderson Signed-off-by: Paolo Bonzini Reviewed-by: David Hildenbrand --- 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); \ --=20 2.39.1