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,URIBL_BLOCKED autolearn=unavailable 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 768C6C282D7 for ; Tue, 5 Feb 2019 15:10:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 47425217D6 for ; Tue, 5 Feb 2019 15:10:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729644AbfBEPKu (ORCPT ); Tue, 5 Feb 2019 10:10:50 -0500 Received: from smtp.nue.novell.com ([195.135.221.5]:58909 "EHLO smtp.nue.novell.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729184AbfBEPKu (ORCPT ); Tue, 5 Feb 2019 10:10:50 -0500 Received: from [10.160.4.48] (charybdis.suse.de [149.44.162.66]) by smtp.nue.novell.com with ESMTP (TLS encrypted); Tue, 05 Feb 2019 16:10:48 +0100 Subject: Re: Question on handling managed IRQs when hotplugging CPUs To: Keith Busch , John Garry Cc: Hannes Reinecke , Thomas Gleixner , Christoph Hellwig , Marc Zyngier , "axboe@kernel.dk" , Peter Zijlstra , Michael Ellerman , Linuxarm , "linux-kernel@vger.kernel.org" , "linux-scsi@vger.kernel.org" , "linux-block@vger.kernel.org" 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> From: Hannes Reinecke Message-ID: <0de6dae8-1234-3e3f-d8f3-2d8de47b7f9e@suse.com> Date: Tue, 5 Feb 2019 16:10:47 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.3.0 MIME-Version: 1.0 In-Reply-To: <20190205145244.GB28023@localhost.localdomain> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2/5/19 3:52 PM, 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. > Indeed. But we don't provide any mechanisms for that ATM, right? Maybe this would be a topic fit for LSF/MM? Cheers, Hannes -- Dr. Hannes Reinecke zSeries & Storage hare@suse.com +49 911 74053 688 SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg GF: F. Imendörffer, J. Smithard, D. Upmanyu, G. Norton HRB 21284 (AG Nürnberg)