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Tue, 5 Dec 2017 16:08:20 +0000 From: Bart Van Assche To: "linux-scsi@vger.kernel.org" , "hch@infradead.org" , "jejb@linux.vnet.ibm.com" , "linux-block@vger.kernel.org" , "axboe@fb.com" , "ming.lei@redhat.com" , "martin.petersen@oracle.com" CC: "linux-kernel@vger.kernel.org" , "hare@suse.com" , "holger@applied-asynchrony.com" Subject: Re: [PATCH] SCSI: run queue if SCSI device queue isn't ready and queue is idle Thread-Topic: [PATCH] SCSI: run queue if SCSI device queue isn't ready and queue is idle Thread-Index: AQHTbZ4g7T3yQq9yCkKeO51Qk7DLeaM060uA Date: Tue, 5 Dec 2017 16:08:20 +0000 Message-ID: <1512490099.2660.6.camel@sandisk.com> References: <20171205075256.10319-1-ming.lei@redhat.com> In-Reply-To: <20171205075256.10319-1-ming.lei@redhat.com> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: authentication-results: spf=none (sender IP is ) smtp.mailfrom=Bart.VanAssche@wdc.com; x-originating-ip: [199.255.44.171] x-ms-publictraffictype: Email x-microsoft-exchange-diagnostics: 1; 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SRVR:CY1PR0401MB1535; BCL:0; PCL:0; RULEID:(100000803101)(100110400095); SRVR:CY1PR0401MB1535; x-forefront-prvs: 0512CC5201 x-forefront-antispam-report: SFV:NSPM; SFS:(10019020)(6009001)(366004)(376002)(346002)(39860400002)(377424004)(24454002)(189002)(199003)(3280700002)(3660700001)(53936002)(33896003)(2906002)(6246003)(97736004)(229853002)(2950100002)(99286004)(2501003)(316002)(2201001)(77096006)(4326008)(6486002)(5660300001)(110136005)(14454004)(54906003)(7736002)(6436002)(76176011)(86362001)(68736007)(305945005)(7416002)(6506006)(25786009)(8676002)(36756003)(2900100001)(101416001)(103116003)(478600001)(189998001)(105586002)(33646002)(81166006)(8936002)(9686003)(106356001)(102836003)(6512007)(66066001)(81156014)(3846002)(6116002)(72206003); DIR:OUT; SFP:1102; SCL:1; SRVR:CY1PR0401MB1535; H:CY1PR0401MB1536.namprd04.prod.outlook.com; FPR:; SPF:None; PTR:InfoNoRecords; MX:1; A:1; LANG:en; spamdiagnosticoutput: 1:99 spamdiagnosticmetadata: NSPM Content-ID: <0C64A389DF03B445955E906C4745E347@namprd04.prod.outlook.com> MIME-Version: 1.0 X-OriginatorOrg: wdc.com X-MS-Exchange-CrossTenant-Network-Message-Id: ea624bef-1972-44f8-1a6c-08d53bfa676b X-MS-Exchange-CrossTenant-originalarrivaltime: 05 Dec 2017 16:08:20.4478 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: b61c8803-16f3-4c35-9b17-6f65f441df86 X-MS-Exchange-Transport-CrossTenantHeadersStamped: CY1PR0401MB1535 Sender: linux-scsi-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-scsi@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP On Tue, 2017-12-05 at 15:52 +0800, Ming Lei wrote: > diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c > index db9556662e27..1816dd8259b3 100644 > --- a/drivers/scsi/scsi_lib.c > +++ b/drivers/scsi/scsi_lib.c > @@ -1967,6 +1967,8 @@ static bool scsi_mq_get_budget(struct blk_mq_hw_ctx *hctx) > out_put_device: > put_device(&sdev->sdev_gendev); > out: > + if (atomic_read(&sdev->device_busy) == 0 && !scsi_device_blocked(sdev)) > + blk_mq_delay_run_hw_queue(hctx, SCSI_QUEUE_DELAY); > return false; > } This cannot work since multiple threads can call scsi_mq_get_budget() concurrently and hence it can happen that none of them sees atomic_read(&sdev->device_busy) == 0. BTW, the above patch is something I consider as a workaround. Have you considered to fix the root cause and to add blk_mq_sched_mark_restart_hctx() where these are missing, e.g. in blk_mq_sched_dispatch_requests()? The patch below is not a full solution but resulted in a significant improvement in my tests: Bart. Reviewed-by: Bart Van Assche diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c index 69e3226e66ca..9d86876ec503 100644 --- a/block/blk-mq-sched.c +++ b/block/blk-mq-sched.c @@ -226,6 +226,7 @@ void blk_mq_sched_dispatch_requests(struct blk_mq_hw_ctx *hctx) * TODO: get more budgets, and dequeue more requests in * one time. */ + blk_mq_sched_mark_restart_hctx(hctx); blk_mq_do_dispatch_ctx(hctx); } else { blk_mq_flush_busy_ctxs(hctx, &rq_list);