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dkim=none (message not signed) header.d=none;nongnu.org; dmarc=none action=none header.from=virtuozzo.com; Received: from AM7PR08MB5494.eurprd08.prod.outlook.com (2603:10a6:20b:dc::15) by AM6PR08MB3623.eurprd08.prod.outlook.com (2603:10a6:20b:48::23) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4129.25; Fri, 21 May 2021 15:56:07 +0000 Received: from AM7PR08MB5494.eurprd08.prod.outlook.com ([fe80::b403:c1a9:6bb7:133]) by AM7PR08MB5494.eurprd08.prod.outlook.com ([fe80::b403:c1a9:6bb7:133%8]) with mapi id 15.20.4150.025; Fri, 21 May 2021 15:56:07 +0000 Subject: Re: [PATCH v2 6/7] block-copy: atomic .cancelled and .finished fields in BlockCopyCallState To: Paolo Bonzini , Emanuele Giuseppe Esposito , qemu-block@nongnu.org Cc: John Snow , Kevin Wolf , Max Reitz , Stefan Hajnoczi , qemu-devel@nongnu.org References: <20210518100757.31243-1-eesposit@redhat.com> <20210518100757.31243-7-eesposit@redhat.com> <068832dd-c577-0234-4a1d-dfdae6a5b4dd@virtuozzo.com> <05e94bee-8ee8-e23f-19c1-a7fcb540e080@redhat.com> From: Vladimir Sementsov-Ogievskiy Message-ID: <9dd72513-87f6-bb54-2364-35e767e903e4@virtuozzo.com> Date: Fri, 21 May 2021 18:56:05 +0300 User-Agent: Mozilla/5.0 (X11; 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envelope-from=vsementsov@virtuozzo.com; helo=EUR04-VI1-obe.outbound.protection.outlook.com X-Spam_score_int: -27 X-Spam_score: -2.8 X-Spam_bar: -- X-Spam_report: (-2.8 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, MSGID_FROM_MTA_HEADER=0.001, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_PASS=-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: 2.1.23 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" 21.05.2021 18:02, Paolo Bonzini wrote: > On 20/05/21 17:34, Vladimir Sementsov-Ogievskiy wrote: >> >>> By adding acquire/release pairs, we ensure that .ret and .error_is_read >>> fields are written by block_copy_dirty_clusters before .finished is true. >> >> As I already said, please, can we live with one mutex for now? finished, ret, error_is_read, all these variables are changing rarely. I doubt that performance is improved by these atomic operations. But complexity of the architecture increases exponentially. > > The problem is that these are used outside coroutines. load-acquire/store-release is the simplest way to handle a "finished" flag really. > Related, maybe we can support CoMutex outside of coroutine context? Create a coroutine, which will lock the mutex and unlock it for us... Or something like this.. It will help the task of making everything thread-safe a lot -- Best regards, Vladimir