From patchwork Thu Jul 21 09:24:17 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Christoph Hellwig X-Patchwork-Id: 9241295 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id 5F83360756 for ; Thu, 21 Jul 2016 09:24:30 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 4B9D326242 for ; Thu, 21 Jul 2016 09:24:30 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 3F9A027A98; Thu, 21 Jul 2016 09:24:30 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.9 required=2.0 tests=BAYES_00,RCVD_IN_DNSWL_HI autolearn=ham version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id B49E127BFC for ; Thu, 21 Jul 2016 09:24:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751631AbcGUJY3 (ORCPT ); Thu, 21 Jul 2016 05:24:29 -0400 Received: from bombadil.infradead.org ([198.137.202.9]:55062 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751588AbcGUJY2 (ORCPT ); Thu, 21 Jul 2016 05:24:28 -0400 Received: from [83.175.99.196] (helo=localhost) by bombadil.infradead.org with esmtpsa (Exim 4.85_2 #1 (Red Hat Linux)) id 1bQADS-0000UW-PF; Thu, 21 Jul 2016 09:24:27 +0000 From: Christoph Hellwig To: axboe@fb.com, agordeev@redhat.com, linux-block@vger.kernel.org Subject: [PATCH 1/3] blk-mq: don't redistribute hardware queues on a CPU hotplug event Date: Thu, 21 Jul 2016 11:24:17 +0200 Message-Id: <1469093059-24594-2-git-send-email-hch@lst.de> X-Mailer: git-send-email 2.1.4 In-Reply-To: <1469093059-24594-1-git-send-email-hch@lst.de> References: <1469093059-24594-1-git-send-email-hch@lst.de> X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org. See http://www.infradead.org/rpr.html Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP Currently blk-mq will totally remap hardware context when a CPU hotplug even happened, which causes major havoc for drivers, as they are never told about this remapping. E.g. any carefully sorted out CPU affinity will just be completely messed up. The rebuild also doesn't really help for the common case of cpu hotplug, which is soft onlining / offlining of cpus - in this case we should just leave the queue and irq mapping as is. If it actually worked it would have helped in the case of physical cpu hotplug, although for that we'd need a way to actually notify the driver. Note that drivers may already be able to accommodate such a topology change on their own, e.g. using the reset_controller sysfs file in NVMe will cause the driver to get things right for this case. With the rebuild removed we will simplify retain the queue mapping for a soft offlined CPU that will work when it comes back online, and will map any newly onlined CPU to queue NULL until the driver initiates a rebuild of the queue map. Signed-off-by: Christoph Hellwig --- block/blk-mq.c | 2 -- 1 file changed, 2 deletions(-) diff --git a/block/blk-mq.c b/block/blk-mq.c index 576e711..6e88e2c 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -2156,8 +2156,6 @@ static void blk_mq_queue_reinit(struct request_queue *q, blk_mq_sysfs_unregister(q); - blk_mq_update_queue_map(q->mq_map, q->nr_hw_queues, online_mask); - /* * redo blk_mq_init_cpu_queues and blk_mq_init_hw_queues. FIXME: maybe * we should change hctx numa_node according to new topology (this