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=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT 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 B048EC282CC for ; Tue, 5 Feb 2019 15:11:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7DEC2217D6 for ; Tue, 5 Feb 2019 15:11:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729674AbfBEPLz (ORCPT ); Tue, 5 Feb 2019 10:11:55 -0500 Received: from mga09.intel.com ([134.134.136.24]:25492 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729184AbfBEPLy (ORCPT ); Tue, 5 Feb 2019 10:11:54 -0500 X-Amp-Result: UNSCANNABLE X-Amp-File-Uploaded: False Received: from orsmga001.jf.intel.com ([10.7.209.18]) by orsmga102.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 05 Feb 2019 07:11:49 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.56,564,1539673200"; d="scan'208";a="136069744" Received: from unknown (HELO localhost.localdomain) ([10.232.112.69]) by orsmga001.jf.intel.com with ESMTP; 05 Feb 2019 07:11:48 -0800 Date: Tue, 5 Feb 2019 08:11:15 -0700 From: Keith Busch To: John Garry 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" Subject: Re: Question on handling managed IRQs when hotplugging CPUs Message-ID: <20190205151115.GC28023@localhost.localdomain> References: <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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.9.1 (2017-09-22) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Feb 05, 2019 at 03:09:28PM +0000, John Garry wrote: > 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. Then they'll need to register their own CPU notifiers and handle the ones they dispatched.