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 976C2C433FE for ; Mon, 17 Oct 2022 15:31:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231201AbiJQPbM (ORCPT ); Mon, 17 Oct 2022 11:31:12 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33166 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230228AbiJQPbL (ORCPT ); Mon, 17 Oct 2022 11:31:11 -0400 Received: from verein.lst.de (verein.lst.de [213.95.11.211]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2E76A13F1F for ; Mon, 17 Oct 2022 08:31:09 -0700 (PDT) Received: by verein.lst.de (Postfix, from userid 2407) id 5514B68C4E; Mon, 17 Oct 2022 17:31:05 +0200 (CEST) Date: Mon, 17 Oct 2022 17:31:05 +0200 From: Christoph Hellwig To: "Paul E. McKenney" Cc: Christoph Hellwig , Chao Leng , linux-nvme@lists.infradead.org, linux-block@vger.kernel.org, sagi@grimberg.me, kbusch@kernel.org, ming.lei@redhat.com, axboe@kernel.dk Subject: Re: [PATCH v2 1/2] blk-mq: add tagset quiesce interface Message-ID: <20221017153105.GA32509@lst.de> References: <20221013094450.5947-1-lengchao@huawei.com> <20221013094450.5947-2-lengchao@huawei.com> <20221017133906.GA24492@lst.de> <20221017152136.GI5600@paulmck-ThinkPad-P17-Gen-1> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20221017152136.GI5600@paulmck-ThinkPad-P17-Gen-1> 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 08:21:36AM -0700, Paul E. McKenney wrote: > The main reason for having multiple srcu_struct structures is to > prevent the readers from one from holding up the updaters from another. > Except that by waiting for the multiple grace periods, you are losing > that property anyway, correct? Or is this code waiting on only a small > fraction of the srcu_struct structures associated with blk_queue? There are a few places that do this. SCSI and MMC could probably switch to this scheme or at least and open coded version of it (if we move to a per_tagsect srcu_struct open coding it might be a better idea anyway). del_gendisk is one where we have to go one queue at a time, and that might actually matter for a device removal. elevator_switch is another one, there is a variant for it that works on the whole tagset, but also those that don't.