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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS autolearn=ham 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 201EBC282CB for ; Tue, 5 Feb 2019 15:09:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id EBBA5217F9 for ; Tue, 5 Feb 2019 15:09:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729573AbfBEPJv (ORCPT ); Tue, 5 Feb 2019 10:09:51 -0500 Received: from szxga05-in.huawei.com ([45.249.212.191]:3269 "EHLO huawei.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726646AbfBEPJv (ORCPT ); Tue, 5 Feb 2019 10:09:51 -0500 Received: from DGGEMS412-HUB.china.huawei.com (unknown [172.30.72.60]) by Forcepoint Email with ESMTP id 8FB51A55CE186248818A; Tue, 5 Feb 2019 23:09:47 +0800 (CST) Received: from [127.0.0.1] (10.202.227.238) by DGGEMS412-HUB.china.huawei.com (10.3.19.212) with Microsoft SMTP Server id 14.3.408.0; Tue, 5 Feb 2019 23:09:36 +0800 Subject: Re: Question on handling managed IRQs when hotplugging CPUs To: Keith Busch References: <20190129154433.GF15302@localhost.localdomain> <757902fc-a9ea-090b-7853-89944a0ce1b5@huawei.com> <20190129172059.GC17132@localhost.localdomain> <3fe63dab-0791-f476-69c4-9866b70e8520@huawei.com> <86d5028d-44ab-3696-f7fe-828d7655faa9@huawei.com> <745609be-b215-dd2d-c31f-0bd84572f49f@suse.de> <42d149c5-0380-c357-8811-81015159ac04@huawei.com> <20190205145244.GB28023@localhost.localdomain> CC: Hannes Reinecke , Thomas Gleixner , Christoph Hellwig , Marc Zyngier , "axboe@kernel.dk" , Peter Zijlstra , Michael Ellerman , Linuxarm , "linux-kernel@vger.kernel.org" , "Hannes Reinecke" , "linux-scsi@vger.kernel.org" , "linux-block@vger.kernel.org" From: John Garry Message-ID: Date: Tue, 5 Feb 2019 15:09:28 +0000 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:45.0) Gecko/20100101 Thunderbird/45.3.0 MIME-Version: 1.0 In-Reply-To: <20190205145244.GB28023@localhost.localdomain> Content-Type: text/plain; charset="windows-1252"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [10.202.227.238] X-CFilter-Loop: Reflected Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On 05/02/2019 14:52, Keith Busch wrote: > On Tue, Feb 05, 2019 at 05:24:11AM -0800, John Garry wrote: >> On 04/02/2019 07:12, Hannes Reinecke wrote: >> >> Hi Hannes, >> >>> >>> So, as the user then has to wait for the system to declars 'ready for >>> CPU remove', why can't we just disable the SQ and wait for all I/O to >>> complete? >>> We can make it more fine-grained by just waiting on all outstanding I/O >>> on that SQ to complete, but waiting for all I/O should be good as an >>> initial try. >>> With that we wouldn't need to fiddle with driver internals, and could >>> make it pretty generic. >> >> I don't fully understand this idea - specifically, at which layer would >> we be waiting for all the IO to complete? > > Whichever layer dispatched the IO to a CPU specific context should > be the one to wait for its completion. That should be blk-mq for most > block drivers. For SCSI devices, unfortunately not all IO sent to the HW originates from blk-mq or any other single entity. Thanks, John > > . >