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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id E2C0CC4332F for ; Mon, 17 Oct 2022 15:31:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=/EUsESql93tn6dVCOadSawA/ezkRYy3il9jfNAY/jBs=; b=LzYswFlcTmuSE5ne5A9Rdvtl7o UhdxP4YTSjCt3OLIdHj6dMiMuXQNjHkefmjSjQ6AvSiFi9DvQYvSvUc5rOiRP2K9GZh5YPmAw+AeM ozJf5uEyjXVVckFAm6Y5UpJ3n1GwdrPdABnRwJDPWqh0Odt1a/9O1W8Bm1+nG7xjBQ2OZFvqgO8FU WwQm5uAUCSkW7GoPn5kX7R5LznwvvRDUa9yTv4XfAViDtxCZADPkYBGnOCdBb5xKBouezEpvXprjF /QcrJWsAzM9aoZEyfkFtl9b+3jaXebX3x8NDAhlz4S8wCjB3rk/Doygu/pT97ZHCYCC907hllJWqY ctdRrsAA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1okS5D-00DGoT-DZ; Mon, 17 Oct 2022 15:31:15 +0000 Received: from verein.lst.de ([213.95.11.211]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1okS59-00DGkx-JI for linux-nvme@lists.infradead.org; Mon, 17 Oct 2022 15:31:12 +0000 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) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20221017_083111_822008_40D1648B X-CRM114-Status: GOOD ( 16.44 ) X-BeenThere: linux-nvme@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "Linux-nvme" Errors-To: linux-nvme-bounces+linux-nvme=archiver.kernel.org@lists.infradead.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.