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dkim=none (message not signed) header.d=none;redhat.com; dmarc=none action=none header.from=virtuozzo.com; Received: from AM7PR08MB5494.eurprd08.prod.outlook.com (2603:10a6:20b:dc::15) by AM6PR08MB3541.eurprd08.prod.outlook.com (2603:10a6:20b:51::31) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4087.35; Wed, 5 May 2021 10:17:54 +0000 Received: from AM7PR08MB5494.eurprd08.prod.outlook.com ([fe80::b403:c1a9:6bb7:133]) by AM7PR08MB5494.eurprd08.prod.outlook.com ([fe80::b403:c1a9:6bb7:133%7]) with mapi id 15.20.4108.026; Wed, 5 May 2021 10:17:54 +0000 Subject: Re: [PATCH] block: simplify write-threshold and drop write notifiers To: Stefan Hajnoczi Cc: qemu-block@nongnu.org, qemu-devel@nongnu.org, fam@euphon.net, mreitz@redhat.com, kwolf@redhat.com, pbonzini@redhat.com, eesposit@redhat.com References: <20210421220950.105017-1-vsementsov@virtuozzo.com> From: Vladimir Sementsov-Ogievskiy Message-ID: <1e872925-2ddd-1072-9d35-d94f9cee63eb@virtuozzo.com> Date: Wed, 5 May 2021 13:17:52 +0300 User-Agent: Mozilla/5.0 (X11; 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envelope-from=vsementsov@virtuozzo.com; helo=EUR01-HE1-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" 05.05.2021 13:10, Stefan Hajnoczi wrote: > On Thu, Apr 22, 2021 at 01:09:50AM +0300, Vladimir Sementsov-Ogievskiy wrote: >> @@ -1981,8 +1985,15 @@ bdrv_co_write_req_prepare(BdrvChild *child, int64_t offset, int64_t bytes, >> } else { >> assert(child->perm & BLK_PERM_WRITE); >> } >> - return notifier_with_return_list_notify(&bs->before_write_notifiers, >> - req); >> + write_threshold = qatomic_read(&bs->write_threshold_offset); >> + if (write_threshold > 0 && offset + bytes > write_threshold) { >> + qapi_event_send_block_write_threshold( >> + bs->node_name, >> + offset + bytes - write_threshold, >> + write_threshold); >> + qatomic_set(&bs->write_threshold_offset, 0); > > It's safer to reset the threshold before emitting the event. That way > there is no race with the QMP client setting a new threshold via > bdrv_write_threshold_is_set(). I guess the race is possible since > qatomic is used and there is no lock. > > I like the idea of dropping write notifiers: > Acked-by: Stefan Hajnoczi > Sorry, this is an outdated patch, I've sent a v2: [PATCH v2 0/9] block: refactor write threshold -- Best regards, Vladimir