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Thu, 2 Aug 2018 15:52:00 +0000 From: Bart Van Assche To: "ming.lei@redhat.com" , "jianchao.w.wang@oracle.com" CC: "linux-kernel@vger.kernel.org" , "linux-block@vger.kernel.org" , "axboe@kernel.dk" Subject: Re: [RFC] blk-mq: clean up the hctx restart Thread-Topic: [RFC] blk-mq: clean up the hctx restart Thread-Index: AQHUKIMWxQ9ytKciREKo5HIno+xAH6SoxRwAgAAGCQCAAA/RAIABT5wAgABwGYCAAgXLAA== Date: Thu, 2 Aug 2018 15:52:00 +0000 Message-ID: <9feaa41702ef6fcc00ce1b8aa19bbe179edf4e3f.camel@wdc.com> References: <1533009735-2221-1-git-send-email-jianchao.w.wang@oracle.com> <20180731045805.GE15701@ming.t460p> <8a3383e6-2926-6858-d8f2-671f3cb9e460@oracle.com> <20180731061616.GF15701@ming.t460p> <42371198-2a4b-1062-3564-411645ffba98@oracle.com> <20180801085841.GA27962@ming.t460p> In-Reply-To: <20180801085841.GA27962@ming.t460p> 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; 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charset="utf-7" Content-ID: Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-OriginatorOrg: wdc.com X-MS-Exchange-CrossTenant-Network-Message-Id: a316d69a-5ec6-4a47-c287-08d5f88fe263 X-MS-Exchange-CrossTenant-originalarrivaltime: 02 Aug 2018 15:52:00.3899 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: b61c8803-16f3-4c35-9b17-6f65f441df86 X-MS-Exchange-Transport-CrossTenantHeadersStamped: MWHPR04MB0622 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 2018-08-01 at 16:58 +-0800, Ming Lei wrote: +AD4- On Wed, Aug 01, 2018 at 10:17:30AM +-0800, jianchao.wang wrote: +AD4- +AD4- However, due to the limits in hctx+AF8-may+AF8-queue, q+AF8-b s= till cannot get the +AD4- +AD4- tags. The RR restart also will not wake up q+AF8-a. +AD4- +AD4- This is unfair for q+AF8-a. +AD4- +AD4-=20 +AD4- +AD4- When we remove RR restart fashion, at least, the q+AF8-a will b= e waked up by +AD4- +AD4- the hctx restart. +AD4- +AD4- Is this the improvement of fairness you said in driver tag allo= cation ? +AD4-=20 +AD4- I mean the fairness is totally covered by the general tag allocation +AD4- algorithm now, which is sort of FIFO style because of waitqueue, but = RR +AD4- restart wakes up queue in the order of request queue. >From sbitmap.h: +ACM-define SBQ+AF8-WAIT+AF8-QUEUES 8 What do you think is the effect of your patch if more than eight LUNs are active and the SCSI queue is full? Thanks, Bart.