Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752581AbbFXQYf (ORCPT ); Wed, 24 Jun 2015 12:24:35 -0400 Received: from mail-ie0-f176.google.com ([209.85.223.176]:36526 "EHLO mail-ie0-f176.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752881AbbFXQY2 (ORCPT ); Wed, 24 Jun 2015 12:24:28 -0400 MIME-Version: 1.0 In-Reply-To: References: <1434894751-6877-1-git-send-email-akinobu.mita@gmail.com> <1434894751-6877-4-git-send-email-akinobu.mita@gmail.com> Date: Thu, 25 Jun 2015 00:24:27 +0800 Message-ID: Subject: Re: [PATCH 3/4] blk-mq: establish new mapping before cpu starts handling requests From: Ming Lei To: Akinobu Mita Cc: Linux Kernel Mailing List , Jens Axboe Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1609 Lines: 35 On Wed, Jun 24, 2015 at 10:34 PM, Akinobu Mita wrote: > Hi Ming, > > 2015-06-24 18:46 GMT+09:00 Ming Lei : >> On Sun, Jun 21, 2015 at 9:52 PM, Akinobu Mita wrote: >>> ctx->index_hw is zero for the CPUs which have never been onlined since >>> the block queue was initialized. If one of those CPUs is hotadded and >>> starts handling request before new mappings are established, pending >> >> Could you explain a bit what the handling request is? The fact is that >> blk_mq_queue_reinit() is run after all queues are put into freezing. > > Notifier callbacks for CPU_ONLINE action can be run on the other CPU > than the CPU which was just onlined. So it is possible for the > process running on the just onlined CPU to insert request and run > hw queue before blk_mq_queue_reinit_notify() is actually called with > action=CPU_ONLINE. You are right because blk_mq_queue_reinit_notify() is alwasy run after the CPU becomes UP, so there is a tiny window in which the CPU is up but the mapping is updated. Per current design, the CPU just onlined is still mapped to hw queue 0 until the mapping is updated by blk_mq_queue_reinit_notify(). But I am wondering why it is a problem and why you think flush_busy_ctxs can't find the requests on the software queue in this situation? -- Ming Lei -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/