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Tue, 7 Apr 2020 09:10:32 +0000 Subject: Re: [PATCH for-5.0 v2 2/3] block: Increase BB.in_flight for coroutine interfaces To: Kevin Wolf References: <20200406171403.6761-1-kwolf@redhat.com> <20200406171403.6761-3-kwolf@redhat.com> <9d0aa9cc-61a1-fd14-357e-6fb0ba2742dd@virtuozzo.com> <20200407085216.GA7695@linux.fritz.box> From: Vladimir Sementsov-Ogievskiy X-Tagtoolbar-Keys: D20200407121030038 Message-ID: Date: Tue, 7 Apr 2020 12:10:30 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.2.1 In-Reply-To: <20200407085216.GA7695@linux.fritz.box> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-ClientProxiedBy: AM6PR0502CA0067.eurprd05.prod.outlook.com (2603:10a6:20b:56::44) To AM7PR08MB5494.eurprd08.prod.outlook.com (2603:10a6:20b:dc::15) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from [192.168.100.2] (185.215.60.160) by AM6PR0502CA0067.eurprd05.prod.outlook.com (2603:10a6:20b:56::44) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.2856.20 via Frontend Transport; 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X-Microsoft-Antispam-Message-Info: Zlc7HPXR42NjIoCvYAsRvsqkQNxSMHjjFmQ9sKPPetmrkB7M8qvKqKHpSVY9fhlPMRzGaAdGl6BHS1pmZE0Em115sT4otNzYAR7RDEWAFgqkfeTUrnFzm5ZR1UYflt++vPJ4LJbU+Umel6EjJ6DG5BSdVm4QGPwFHbUO6vUKqSGwfrhCd7CWx0XGpgEjfC7juY13XKYOVy7btd3yzQYS22LDbAJIFobOcw1nt/O1jw28PEYQ9VDXpjQSH0Y1e9t2TlrIjEAK2phSHFWRFETsSGyXpXREr2xA4lPeTHwdT6/a1vyaqxZ6kISt1J1PacQ8klQnWWG4F1pHgywFGtNyjnaN4Rym+jKvPGf8bnxNAY5A58WOx6WTpKDuGszo5//D/Zqa9HP81qV4R9AeMCoAtvwWhSDGN73fwKY2dxZWzHtpMJeFSz/tUK/g8nkzxUWy X-MS-Exchange-AntiSpam-MessageData: gfyIMqO5/36cq74jWlr1jVzcs9XmZ38DNYNqHllgXv9oNTENVRB9jJRKXoMjoFapkBHhDWCvxfT9Bp8ORFkZJhUZcouVX28LRxHp6psZQh3TTO1Arn2qjFRGrZyzZffm5oPV6p3QObTFJZ4Cte1NKA== X-OriginatorOrg: virtuozzo.com X-MS-Exchange-CrossTenant-Network-Message-Id: fd87f7e2-b073-47ca-fcd8-08d7dad3863e X-MS-Exchange-CrossTenant-OriginalArrivalTime: 07 Apr 2020 09:10:32.2927 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 0bc7f26d-0264-416e-a6fc-8352af79c58f X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: fFtmVPOgLY9SCdpym+9vsYrQKU3Lj9ocn2tf5G/SELlmc/DlVzvwDGH9J+Uovaj38mlEdLuBj+JUdFQz0vpkx3wrEj9EewG+JJyayIWOFGM= X-MS-Exchange-Transport-CrossTenantHeadersStamped: AM7PR08MB5432 X-detected-operating-system: by eggs.gnu.org: Windows NT kernel [generic] [fuzzy] X-Received-From: 40.107.20.99 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: , Cc: qemu-block@nongnu.org, s.reiter@proxmox.com, qemu-devel@nongnu.org, dietmar@proxmox.com, stefanha@redhat.com, mreitz@redhat.com, t.lamprecht@proxmox.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" 07.04.2020 11:52, Kevin Wolf wrote: > Am 07.04.2020 um 08:41 hat Vladimir Sementsov-Ogievskiy geschrieben: >> 06.04.2020 20:14, Kevin Wolf wrote: >>> External callers of blk_co_*() don't currently increase the >>> BlockBackend.in_flight counter, but calls from blk_aio_*() do, so there >>> is an inconsistency whether the counter has been increased or not. >>> >>> This patch moves the actual operations to static functions that can >>> later know they will always be called with in_flight increased exactly >>> once, even for external callers using the blk_co_*() coroutine >>> interfaces. >>> >>> If the public blk_co_*() interface is unused, remove it. >>> >>> Signed-off-by: Kevin Wolf >> >> >> Reviewed-by: Vladimir Sementsov-Ogievskiy >> >> Still, did you consider instead just move inc/dec to _co_ functions, like >> [...] >> (and same for write, ioctl, flush, discard). It seems more >> consistent.. Should it work? > > No, it would be wrong because it would be too late. The main purpose of > blk_inc_in_flight() is to keep the request covered during the first and > the last phase outside of blk_co_*(), which can potentially involve BHs > like blk_aio_complete_bh(). > > Kevin > OK, thanks, I see now, we want to caver possible completion BH. Hmm, not too late but too early (for decrement).. As nothing interesting happening between increment in blk_aio_prwv and entering the coroutine with _do_ function. -- Best regards, Vladimir