From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.4 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 921AAC12002 for ; Wed, 21 Jul 2021 10:01:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 74E2961221 for ; Wed, 21 Jul 2021 10:01:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236867AbhGUJU1 (ORCPT ); Wed, 21 Jul 2021 05:20:27 -0400 Received: from frasgout.his.huawei.com ([185.176.79.56]:3442 "EHLO frasgout.his.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236327AbhGUJEw (ORCPT ); Wed, 21 Jul 2021 05:04:52 -0400 Received: from fraeml712-chm.china.huawei.com (unknown [172.18.147.201]) by frasgout.his.huawei.com (SkyGuard) with ESMTP id 4GV9Kb61r5z6D8nk; Wed, 21 Jul 2021 17:30:11 +0800 (CST) Received: from lhreml724-chm.china.huawei.com (10.201.108.75) by fraeml712-chm.china.huawei.com (10.206.15.61) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2176.2; Wed, 21 Jul 2021 11:44:57 +0200 Received: from [10.47.85.43] (10.47.85.43) by lhreml724-chm.china.huawei.com (10.201.108.75) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2176.2; Wed, 21 Jul 2021 10:44:56 +0100 Subject: Re: [PATCH V4 1/3] driver core: mark device as irq affinity managed if any irq is managed To: Christoph Hellwig , Thomas Gleixner CC: Ming Lei , Jens Axboe , , , "Greg Kroah-Hartman" , Bjorn Helgaas , , Sagi Grimberg , Daniel Wagner , Wen Xiong , Hannes Reinecke , Keith Busch , Marc Zyngier References: <20210715120844.636968-1-ming.lei@redhat.com> <20210715120844.636968-2-ming.lei@redhat.com> <5e534fdc-909e-39b2-521d-31f643a10558@huawei.com> <20210719094414.GC431@lst.de> <87lf60cevz.ffs@nanos.tec.linutronix.de> <20210721072445.GA11257@lst.de> From: John Garry Message-ID: Date: Wed, 21 Jul 2021 10:44:53 +0100 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.12.1 MIME-Version: 1.0 In-Reply-To: <20210721072445.GA11257@lst.de> Content-Type: text/plain; charset="utf-8"; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.47.85.43] X-ClientProxiedBy: lhreml734-chm.china.huawei.com (10.201.108.85) To lhreml724-chm.china.huawei.com (10.201.108.75) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org + Marc On 21/07/2021 08:24, Christoph Hellwig wrote: > On Wed, Jul 21, 2021 at 09:20:00AM +0200, Thomas Gleixner wrote: >>> Just walking the list seems fine to me given that this is not a >>> performance criticial path. But what are the locking implications? >> At the moment there are none because the list is initialized in the >> setup path and never modified afterwards. Though that might change >> sooner than later to fix the virtio wreckage vs. MSI-X. > What is the issue there? Either way, if we keep the helper in the > IRQ code it should be easy to spot for anyone adding the locking. > >>> Also does the above imply this won't work for your platform MSI case? >> The msi descriptors are attached to struct device and independent of >> platform/PCI/whatever. > That's what I assumed, but this text from John suggested there is > something odd about the platform case: > > "Did you consider that for PCI .." > . For this special platform MSI case there is a secondary interrupt controller (called mbigen) which generates the MSI on behalf of the device, which I think the MSI belongs to (and not the device, itself). See "latter case" mentioned in commit 91f90daa4fb2. I think Marc and Thomas can explain this much better than I could. Anyway, as I mentioned earlier, I think that this specific problem is unique and can be solved without using a function which examines the struct device.msi_list . Thanks, John