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Thread-Topic: irq_build_affinity_masks() allocates improper affinity if num_possible_cpus() > num_present_cpus()? Thread-Index: AdabnwA0SBdvouNFQ4iAnKm72ZKc6QAc4+aAABDIuTA= Date: Wed, 7 Oct 2020 03:08:09 +0000 Message-ID: References: <87lfgj6v30.fsf@nanos.tec.linutronix.de> In-Reply-To: <87lfgj6v30.fsf@nanos.tec.linutronix.de> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: msip_labels: MSIP_Label_f42aa342-8706-4288-bd11-ebb85995028c_ActionId=2f1cefce-f90a-4392-8907-2db5c9b0b06e;MSIP_Label_f42aa342-8706-4288-bd11-ebb85995028c_ContentBits=0;MSIP_Label_f42aa342-8706-4288-bd11-ebb85995028c_Enabled=true;MSIP_Label_f42aa342-8706-4288-bd11-ebb85995028c_Method=Standard;MSIP_Label_f42aa342-8706-4288-bd11-ebb85995028c_Name=Internal;MSIP_Label_f42aa342-8706-4288-bd11-ebb85995028c_SetDate=2020-10-07T02:58:14Z;MSIP_Label_f42aa342-8706-4288-bd11-ebb85995028c_SiteId=72f988bf-86f1-41af-91ab-2d7cd011db47; authentication-results: linutronix.de; dkim=none (message not signed) header.d=none;linutronix.de; dmarc=none action=none header.from=microsoft.com; x-originating-ip: [2601:600:a280:7f70:e92f:2b81:6f33:777] x-ms-publictraffictype: Email x-ms-office365-filtering-ht: Tenant x-ms-office365-filtering-correlation-id: 12dfaa24-504f-485a-8c78-08d86a6e38bf x-ms-traffictypediagnostic: KU1P153MB0168: x-ms-exchange-transport-forked: True x-microsoft-antispam-prvs: x-ms-oob-tlc-oobclassifiers: OLM:4714; x-ms-exchange-senderadcheck: 1 x-microsoft-antispam: BCL:0; x-microsoft-antispam-message-info: j+O755Cg1hltxZ72quYpQvpwhos3QvCj3nkIHZZOPJcJkJ/6r1zr1g0Jpx3/TWO0x8BkZgcC06zDiumNrsQcOY/qrp3GVDxmCG1C+q+RnCga1mN8xRHI2fgLKQ8OF372rY7YcFuZISEiblAHp04EsOAC0vIA0TF1RbJlj5MVT3d0Kbk13Yup3BjBtsLl3VygVgSRnQCZPJrp8+TAogFlExzqMwBBOXqIhrB0WyN5o9CYYdmRv0p86tYWEcO97XllEPWt5wzVTlN4SnOAOiiuCKpIo034B5DE4eLKVrmqc2O51vtriND6kiPf2edsvNRd0X4aqZ2zSG9UUBZUL3I81w== x-forefront-antispam-report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:KU1P153MB0120.APCP153.PROD.OUTLOOK.COM;PTR:;CAT:NONE;SFS:(4636009)(366004)(376002)(136003)(346002)(396003)(39860400002)(55016002)(10290500003)(6506007)(52536014)(316002)(5660300002)(4326008)(76116006)(2906002)(8936002)(82960400001)(82950400001)(478600001)(107886003)(8676002)(33656002)(66556008)(64756008)(66476007)(54906003)(86362001)(186003)(66446008)(66946007)(8990500004)(83380400001)(7696005)(9686003)(71200400001)(110136005);DIR:OUT;SFP:1102; x-ms-exchange-antispam-messagedata: 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 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-OriginatorOrg: microsoft.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-AuthSource: KU1P153MB0120.APCP153.PROD.OUTLOOK.COM X-MS-Exchange-CrossTenant-Network-Message-Id: 12dfaa24-504f-485a-8c78-08d86a6e38bf X-MS-Exchange-CrossTenant-originalarrivaltime: 07 Oct 2020 03:08:09.9381 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 72f988bf-86f1-41af-91ab-2d7cd011db47 X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: rJ4WBD8G3716gL5Pnum1ckEuan/hUEJu0TU3XfuHYHHqz9zd/ZyEvQBx6yH5b9INP98EiCYfr9iG5jDrFj4P5g== X-MS-Exchange-Transport-CrossTenantHeadersStamped: KU1P153MB0168 Precedence: bulk List-ID: X-Mailing-List: linux-pci@vger.kernel.org > From: Thomas Gleixner > Sent: Tuesday, October 6, 2020 11:58 AM > > ... > > I pass through an MSI-X-capable PCI device to the Linux VM (which has > > only 1 virtual CPU), and the below code does *not* report any error > > (i.e. pci_alloc_irq_vectors_affinity() returns 2, and request_irq() > > returns 0), but the code does not work: the second MSI-X interrupt is n= ot > > happening while the first interrupt does work fine. > > > > int nr_irqs =3D 2; > > int i, nvec, irq; > > > > nvec =3D pci_alloc_irq_vectors_affinity(pdev, nr_irqs, nr_irqs, > > PCI_IRQ_MSIX | PCI_IRQ_AFFINITY, NULL); >=20 > Why should it return an error? The above code returns -ENOSPC if num_possible_cpus() is also 1, and returns 0 if num_possible_cpus() is 128. So it looks the above code is not using the API correctly, and hence gets undefined results. > > for (i =3D 0; i < nvec; i++) { > > irq =3D pci_irq_vector(pdev, i); > > err =3D request_irq(irq, test_intr, 0, "test_intr", &intr_cxt[i= ]); > > } >=20 > And why do you expect that the second interrupt works? >=20 > This is about managed interrupts and the spreading code has two vectors > to which it can spread the interrupts. One is assigned to one half of > the possible CPUs and the other one to the other half. Now you have only > one CPU online so only the interrupt with has the online CPU in the > assigned affinity mask is started up. >=20 > That's how managed interrupts work. If you don't want managed interrupts > then don't use them. >=20 > Thanks, >=20 > tglx Thanks for the clarification! It looks with PCI_IRQ_AFFINITY the kernel=20 guarantees that the allocated interrutps are 1:1 bound to CPUs, and the userspace is unable to change the affinities. This is very useful to suppor= t per-CPU I/O queues. Thanks, -- Dexuan