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Thu, 10 Jun 2021 00:29:17 +0000 From: Damien Le Moal To: Bart Van Assche , Jens Axboe CC: "linux-block@vger.kernel.org" , Christoph Hellwig , Jaegeuk Kim , Hannes Reinecke , Ming Lei , Johannes Thumshirn , Himanshu Madhani Subject: Re: [PATCH 04/14] block: Introduce the ioprio rq-qos policy Thread-Topic: [PATCH 04/14] block: Introduce the ioprio rq-qos policy Thread-Index: AQHXXLsKSREg/Ans2U2BHuooV0bmLg== Date: Thu, 10 Jun 2021 00:29:17 +0000 Message-ID: References: <20210608230703.19510-1-bvanassche@acm.org> <20210608230703.19510-5-bvanassche@acm.org> <98dbb3dc-d925-f2a8-7f34-94f9c56bb257@acm.org> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: authentication-results: acm.org; dkim=none (message not signed) header.d=none;acm.org; dmarc=none action=none header.from=wdc.com; x-originating-ip: [129.253.182.60] x-ms-publictraffictype: Email x-ms-office365-filtering-correlation-id: 137713d2-f708-4da5-1064-08d92ba6c88c x-ms-traffictypediagnostic: DM6PR04MB4348: x-ms-exchange-transport-forked: True x-microsoft-antispam-prvs: wdcipoutbound: EOP-TRUE x-ms-oob-tlc-oobclassifiers: OLM:10000; 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charset="us-ascii" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-OriginatorOrg: wdc.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-AuthSource: DM6PR04MB7081.namprd04.prod.outlook.com X-MS-Exchange-CrossTenant-Network-Message-Id: 137713d2-f708-4da5-1064-08d92ba6c88c X-MS-Exchange-CrossTenant-originalarrivaltime: 10 Jun 2021 00:29:17.8535 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: b61c8803-16f3-4c35-9b17-6f65f441df86 X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: MLsfw/9LJ22sP8yiQiC44jOUk04MY6ljnbAXoGEUGJYRy+iaY+FGmLOz8RuHAcuh2AFc8rqsSPBaCcSKszukeQ== X-MS-Exchange-Transport-CrossTenantHeadersStamped: DM6PR04MB4348 Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On 2021/06/10 1:49, Bart Van Assche wrote:=0A= > On 6/8/21 9:40 PM, Damien Le Moal wrote:=0A= >> On 2021/06/09 8:07, Bart Van Assche wrote:=0A= > =0A= > [ ... ]=0A= > =0A= >>> +/*=0A= >>> + * The accepted I/O priority values are 0..IOPRIO_CLASS_MAX(3). 0 (def= ault)=0A= >>> + * means do not modify the I/O priority. Values 1..3 are used to restr= ict the=0A= >>> + * I/O priority for a cgroup to the specified priority. See also=0A= >>> + * .=0A= >>> + */=0A= >>> +#define IOPRIO_CLASS_MAX IOPRIO_CLASS_IDLE=0A= > =0A= > [ ... ]=0A= > =0A= >>> +static int ioprio_set_prio_class(struct cgroup_subsys_state *css,=0A= >>> + struct cftype *cft, u64 val)=0A= >>> +{=0A= >>> + struct ioprio_blkcg *blkcg =3D ioprio_blkcg_from_css(css);=0A= >>> +=0A= >>> + if (val > IOPRIO_CLASS_MAX)=0A= >>> + return -EINVAL;=0A= >>=0A= >> Where is IOPRIO_CLASS_MAX defined ? I do not see it.=0A= > =0A= > Near the start of the new block/blk-ioprio.c file.=0A= =0A= OK. I missed that. Shouldn't this definition be moved to include/linux/iopr= io.h=0A= ? It can be added as the last entry of the class enum.=0A= =0A= > =0A= >> Why not use ioprio_valid() ?=0A= > =0A= > The definition of that macro is as follows:=0A= > =0A= > #define ioprio_valid(mask) \=0A= > (IOPRIO_PRIO_CLASS((mask)) !=3D IOPRIO_CLASS_NONE)=0A= > =0A= > So that macro accepts I/O priority classes 1..7 while the above code=0A= > accepts I/O priority classes 0..3. I think that ioprio_set_prio_class()= =0A= > should only accept I/O priority class values 0..3.=0A= =0A= Yes. I misread this macro definition. The name is actually confusing. It do= es=0A= not check that the ioprio is valid, it only check that it is not NONE, mean= ing=0A= that something is set, but that something may not be valid. We could probab= ly=0A= turn this macro into an inline function that does a better job at checking = that=0A= valid values are in the "mask" argument, which by the way is also badly nam= ed,=0A= since that is not a mask at all, but an ioprio.=0A= =0A= =0A= =0A= -- =0A= Damien Le Moal=0A= Western Digital Research=0A=