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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2534EC433FE for ; Mon, 17 Oct 2022 13:42:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229712AbiJQNmu (ORCPT ); Mon, 17 Oct 2022 09:42:50 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33882 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229592AbiJQNmt (ORCPT ); Mon, 17 Oct 2022 09:42:49 -0400 Received: from verein.lst.de (verein.lst.de [213.95.11.211]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 86295F02F for ; Mon, 17 Oct 2022 06:42:48 -0700 (PDT) Received: by verein.lst.de (Postfix, from userid 2407) id AE02868BFE; Mon, 17 Oct 2022 15:42:44 +0200 (CEST) Date: Mon, 17 Oct 2022 15:42:44 +0200 From: Christoph Hellwig To: Chao Leng Cc: linux-nvme@lists.infradead.org, linux-block@vger.kernel.org, hch@lst.de, sagi@grimberg.me, kbusch@kernel.org, ming.lei@redhat.com, axboe@kernel.dk, "Paul E. McKenney" Subject: Re: [PATCH v2 1/2] blk-mq: add tagset quiesce interface Message-ID: <20221017134244.GA24775@lst.de> References: <20221013094450.5947-1-lengchao@huawei.com> <20221013094450.5947-2-lengchao@huawei.com> <20221017133906.GA24492@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20221017133906.GA24492@lst.de> User-Agent: Mutt/1.5.17 (2007-11-01) Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On Mon, Oct 17, 2022 at 03:39:06PM +0200, Christoph Hellwig wrote: > Having to allocate a struct rcu_synchronize for each of the potentially > many queues here is a bit sad. > > Pull just explained the start_poll_synchronize_rcu interfaces at ALPSS > last week, so I wonder if something like that would also be feasible > for SRCU, as that would come in really handy here. Alternatively I wonder if we could simply use a single srcu_struct in the tag_set instead of one per-queue. That would potentially increase the number of read side critical sections blk_mq_wait_quiesce_done would have to wait for in tagsets with multiple queues, but I wonder how much overhead that would be in practive.