From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: From: Bart Van Assche To: "tj@kernel.org" , "axboe@kernel.dk" CC: "linux-kernel@vger.kernel.org" , "peterz@infradead.org" , "linux-block@vger.kernel.org" , "kernel-team@fb.com" , "oleg@redhat.com" , "hch@lst.de" , "jianchao.w.wang@oracle.com" , "osandov@fb.com" Subject: Re: [PATCH 2/6] blk-mq: replace timeout synchronization with a RCU and generation based scheme Date: Tue, 12 Dec 2017 21:37:11 +0000 Message-ID: <1513114630.2999.48.camel@wdc.com> References: <20171212190134.535941-1-tj@kernel.org> <20171212190134.535941-3-tj@kernel.org> In-Reply-To: <20171212190134.535941-3-tj@kernel.org> Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 List-ID: T24gVHVlLCAyMDE3LTEyLTEyIGF0IDExOjAxIC0wODAwLCBUZWp1biBIZW8gd3JvdGU6DQo+ICsv Kg0KPiArICogQml0cyBmb3IgcmVxdWVzdC0+Z3N0YXRlLiAgVGhlIGxvd2VyIHR3byBiaXRzIGNh cnJ5IE1RX1JRXyogc3RhdGUgdmFsdWUNCj4gKyAqIGFuZCB0aGUgdXBwZXIgYml0cyB0aGUgZ2Vu ZXJhdGlvbiBudW1iZXIuDQo+ICsgKi8NCj4gK2VudW0gbXFfcnFfc3RhdGUgew0KPiArCU1RX1JR X0lETEUJCT0gMCwNCj4gKwlNUV9SUV9JTl9GTElHSFQJCT0gMSwNCj4gKw0KPiArCU1RX1JRX1NU QVRFX0JJVFMJPSAyLA0KPiArCU1RX1JRX1NUQVRFX01BU0sJPSAoMSA8PCBNUV9SUV9TVEFURV9C SVRTKSAtIDEsDQo+ICsJTVFfUlFfR0VOX0lOQwkJPSAxIDw8IE1RX1JRX1NUQVRFX0JJVFMsDQo+ ICt9Ow0KPiArDQo+IEBAIC04NSw2ICs5OCwzOCBAQCBleHRlcm4gdm9pZCBibGtfbXFfcnFfdGlt ZWRfb3V0KHN0cnVjdCByZXF1ZXN0ICpyZXEsIGJvb2wgcmVzZXJ2ZWQpOw0KPiArLyoqDQo+ICsg KiBibGtfbXFfcnFfc3RhdGUoKSAtIHJlYWQgdGhlIGN1cnJlbnQgTVFfUlFfKiBzdGF0ZSBvZiBh IHJlcXVlc3QNCj4gKyAqIEBycTogdGFyZ2V0IHJlcXVlc3QuDQo+ICsgKi8NCj4gK3N0YXRpYyBp bmxpbmUgaW50IGJsa19tcV9ycV9zdGF0ZShzdHJ1Y3QgcmVxdWVzdCAqcnEpDQo+ICt7DQo+ICsJ cmV0dXJuIFJFQURfT05DRShycS0+Z3N0YXRlKSAmIE1RX1JRX1NUQVRFX01BU0s7DQo+ICt9DQo+ ICsNCj4gKy8qKg0KPiArICogYmxrX21xX3JxX3VwZGF0ZV9zdGF0ZSgpIC0gc2V0IHRoZSBjdXJy ZW50IE1RX1JRXyogc3RhdGUgb2YgYSByZXF1ZXN0DQo+ICsgKiBAcnE6IHRhcmdldCByZXF1ZXN0 Lg0KPiArICogQHN0YXRlOiBuZXcgc3RhdGUgdG8gc2V0Lg0KPiArICoNCj4gKyAqIFNldCBAcnEn cyBzdGF0ZSB0byBAc3RhdGUuICBUaGUgY2FsbGVyIGlzIHJlc3BvbnNpYmxlIGZvciBlbnN1cmlu ZyB0aGF0DQo+ICsgKiB0aGVyZSBhcmUgbm8gb3RoZXIgdXBkYXRlcnMuICBBIHJlcXVlc3QgY2Fu IHRyYW5zaXRpb24gaW50byBJTl9GTElHSFQNCj4gKyAqIG9ubHkgZnJvbSBJRExFIGFuZCBkb2lu ZyBzbyBpbmNyZW1lbnRzIHRoZSBnZW5lcmF0aW9uIG51bWJlci4NCj4gKyAqLw0KPiArc3RhdGlj IGlubGluZSB2b2lkIGJsa19tcV9ycV91cGRhdGVfc3RhdGUoc3RydWN0IHJlcXVlc3QgKnJxLA0K PiArCQkJCQkgIGVudW0gbXFfcnFfc3RhdGUgc3RhdGUpDQo+ICt7DQo+ICsJdTY0IG5ld192YWwg PSAoUkVBRF9PTkNFKHJxLT5nc3RhdGUpICYgfk1RX1JRX1NUQVRFX01BU0spIHwgc3RhdGU7DQo+ ICsNCj4gKwlpZiAoc3RhdGUgPT0gTVFfUlFfSU5fRkxJR0hUKSB7DQo+ICsJCVdBUk5fT05fT05D RShibGtfbXFfcnFfc3RhdGUocnEpICE9IE1RX1JRX0lETEUpOw0KPiArCQluZXdfdmFsICs9IE1R X1JRX0dFTl9JTkM7DQo+ICsJfQ0KPiArDQo+ICsJLyogYXZvaWQgZXhwb3NpbmcgaW50ZXJpbSB2 YWx1ZXMgKi8NCj4gKwlXUklURV9PTkNFKHJxLT5nc3RhdGUsIG5ld192YWwpOw0KPiArfQ0KDQpI ZWxsbyBUZWp1biwNCg0KSGF2ZSB5b3UgY29uc2lkZXJlZCB0aGUgZm9sbG93aW5nIGluc3RlYWQg b2YgaW50cm9kdWNpbmcgTVFfUlFfSURMRSBhbmQNCk1RX1JRX0lOX0ZMSUdIVD8gSSB0aGluayB0 aGlzIGNvdWxkIGhlbHAgdG8gbGltaXQgdGhlIG51bWJlciBvZiBuZXcgYXRvbWljDQpvcGVyYXRp b25zIGludHJvZHVjZWQgaW4gdGhlIGhvdCBwYXRoIGJ5IHRoaXMgcGF0Y2ggc2VyaWVzLg0KDQpz dGF0aWMgaW5saW5lIGJvb2wgYmxrX21xX3JxX2luX2ZsaWdodChzdHJ1Y3QgcmVxdWVzdCAqcnEp DQp7DQoJcmV0dXJuIGxpc3RfZW1wdHkoJnJxLT5xdWV1ZWxpc3QpOw0KfQ0KDQpUaGFua3MsDQoN CkJhcnQu From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752604AbdLLVhU (ORCPT ); Tue, 12 Dec 2017 16:37:20 -0500 Received: from esa3.hgst.iphmx.com ([216.71.153.141]:22546 "EHLO esa3.hgst.iphmx.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752511AbdLLVhR (ORCPT ); Tue, 12 Dec 2017 16:37:17 -0500 X-IronPort-AV: E=Sophos;i="5.45,395,1508774400"; d="scan'208";a="65109892" From: Bart Van Assche To: "tj@kernel.org" , "axboe@kernel.dk" CC: "linux-kernel@vger.kernel.org" , "peterz@infradead.org" , "linux-block@vger.kernel.org" , "kernel-team@fb.com" , "oleg@redhat.com" , "hch@lst.de" , "jianchao.w.wang@oracle.com" , "osandov@fb.com" Subject: Re: [PATCH 2/6] blk-mq: replace timeout synchronization with a RCU and generation based scheme Thread-Topic: [PATCH 2/6] blk-mq: replace timeout synchronization with a RCU and generation based scheme Thread-Index: AQHTc3vSEJieVXIS9EOPhdZv8hd1dKNAO8MA Date: Tue, 12 Dec 2017 21:37:11 +0000 Message-ID: <1513114630.2999.48.camel@wdc.com> References: <20171212190134.535941-1-tj@kernel.org> <20171212190134.535941-3-tj@kernel.org> In-Reply-To: <20171212190134.535941-3-tj@kernel.org> 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;CY1PR0401MB1536;20:AAlapSFHRiJvjIGH7EdScKeueimITaKZ4B8hNmJNnao8q9gyK6kemurmXLA3x2542KpNVrnuOG2PnOLbDYaSNz1SGzsKQ0eApGu2MoTF6LFhqroT4s7ubIp2LFvDGjQxr4yfbBfWcBG74dDFymeuS2mTBB3/3vaa1ziVSqiOcdo= x-ms-exchange-antispam-srfa-diagnostics: SSOS; x-ms-office365-filtering-ht: Tenant x-ms-office365-filtering-correlation-id: 72293c93-bddc-4734-14dc-08d541a88123 x-microsoft-antispam: UriScan:;BCL:0;PCL:0;RULEID:(4534020)(4602075)(4627115)(201703031133081)(201702281549075)(48565401081)(5600026)(4604075)(2017052603307);SRVR:CY1PR0401MB1536; x-ms-traffictypediagnostic: CY1PR0401MB1536: wdcipoutbound: EOP-TRUE x-microsoft-antispam-prvs: x-exchange-antispam-report-test: UriScan:(788757137089); x-exchange-antispam-report-cfa-test: BCL:0;PCL:0;RULEID:(6040450)(2401047)(8121501046)(5005006)(3231023)(93006095)(93001095)(3002001)(10201501046)(6055026)(6041248)(20161123560025)(20161123564025)(20161123555025)(20161123558100)(201703131423075)(201702281528075)(201703061421075)(201703061406153)(20161123562025)(6072148)(201708071742011);SRVR:CY1PR0401MB1536;BCL:0;PCL:0;RULEID:(100000803101)(100110400095);SRVR:CY1PR0401MB1536; x-forefront-prvs: 051900244E x-forefront-antispam-report: SFV:NSPM;SFS:(10019020)(376002)(366004)(39860400002)(346002)(377424004)(189003)(199004)(24454002)(8676002)(81166006)(6246003)(5660300001)(81156014)(6486002)(77096006)(110136005)(54906003)(3280700002)(2950100002)(316002)(3660700001)(97736004)(2906002)(4001150100001)(229853002)(478600001)(7416002)(99286004)(86362001)(6436002)(7736002)(68736007)(103116003)(105586002)(36756003)(53936002)(25786009)(8936002)(305945005)(3846002)(106356001)(66066001)(2900100001)(2501003)(59450400001)(76176011)(14454004)(102836003)(4326008)(6116002)(72206003)(6506007)(6512007);DIR:OUT;SFP:1102;SCL:1;SRVR:CY1PR0401MB1536;H:CY1PR0401MB1536.namprd04.prod.outlook.com;FPR:;SPF:None;PTR:InfoNoRecords;MX:1;A:1;LANG:en; spamdiagnosticoutput: 1:99 spamdiagnosticmetadata: NSPM Content-Type: text/plain; charset="utf-8" Content-ID: MIME-Version: 1.0 X-OriginatorOrg: wdc.com X-MS-Exchange-CrossTenant-Network-Message-Id: 72293c93-bddc-4734-14dc-08d541a88123 X-MS-Exchange-CrossTenant-originalarrivaltime: 12 Dec 2017 21:37:11.8570 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: b61c8803-16f3-4c35-9b17-6f65f441df86 X-MS-Exchange-Transport-CrossTenantHeadersStamped: CY1PR0401MB1536 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: 8bit X-MIME-Autoconverted: from base64 to 8bit by nfs id vBCLbPJS023633 On Tue, 2017-12-12 at 11:01 -0800, Tejun Heo wrote: > +/* > + * Bits for request->gstate. The lower two bits carry MQ_RQ_* state value > + * and the upper bits the generation number. > + */ > +enum mq_rq_state { > + MQ_RQ_IDLE = 0, > + MQ_RQ_IN_FLIGHT = 1, > + > + MQ_RQ_STATE_BITS = 2, > + MQ_RQ_STATE_MASK = (1 << MQ_RQ_STATE_BITS) - 1, > + MQ_RQ_GEN_INC = 1 << MQ_RQ_STATE_BITS, > +}; > + > @@ -85,6 +98,38 @@ extern void blk_mq_rq_timed_out(struct request *req, bool reserved); > +/** > + * blk_mq_rq_state() - read the current MQ_RQ_* state of a request > + * @rq: target request. > + */ > +static inline int blk_mq_rq_state(struct request *rq) > +{ > + return READ_ONCE(rq->gstate) & MQ_RQ_STATE_MASK; > +} > + > +/** > + * blk_mq_rq_update_state() - set the current MQ_RQ_* state of a request > + * @rq: target request. > + * @state: new state to set. > + * > + * Set @rq's state to @state. The caller is responsible for ensuring that > + * there are no other updaters. A request can transition into IN_FLIGHT > + * only from IDLE and doing so increments the generation number. > + */ > +static inline void blk_mq_rq_update_state(struct request *rq, > + enum mq_rq_state state) > +{ > + u64 new_val = (READ_ONCE(rq->gstate) & ~MQ_RQ_STATE_MASK) | state; > + > + if (state == MQ_RQ_IN_FLIGHT) { > + WARN_ON_ONCE(blk_mq_rq_state(rq) != MQ_RQ_IDLE); > + new_val += MQ_RQ_GEN_INC; > + } > + > + /* avoid exposing interim values */ > + WRITE_ONCE(rq->gstate, new_val); > +} Hello Tejun, Have you considered the following instead of introducing MQ_RQ_IDLE and MQ_RQ_IN_FLIGHT? I think this could help to limit the number of new atomic operations introduced in the hot path by this patch series. static inline bool blk_mq_rq_in_flight(struct request *rq) { return list_empty(&rq->queuelist); } Thanks, Bart.