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 1CD3DC4332F for ; Tue, 18 Oct 2022 05:20:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229919AbiJRFUD (ORCPT ); Tue, 18 Oct 2022 01:20:03 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48726 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229934AbiJRFUC (ORCPT ); Tue, 18 Oct 2022 01:20:02 -0400 Received: from verein.lst.de (verein.lst.de [213.95.11.211]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 23EC823EA7 for ; Mon, 17 Oct 2022 22:20:00 -0700 (PDT) Received: by verein.lst.de (Postfix, from userid 2407) id 0F39B68C4E; Tue, 18 Oct 2022 07:19:56 +0200 (CEST) Date: Tue, 18 Oct 2022 07:19:56 +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: <20221018051956.GA18802@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> <20221017153105.GA32509@lst.de> <20221017224115.GJ5600@paulmck-ThinkPad-P17-Gen-1> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20221017224115.GJ5600@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 03:41:15PM -0700, Paul E. McKenney wrote: > Then the big question is "how long do the SRCU readers run?" > > If all of the readers ran for exactly the same duration, there would be > little point in having more than one srcu_struct. The SRCU readers are the I/O dispatch, which will have quite similar runtimes for the different queues. > If the kernel knew up front how long the SRCU readers for a given entry > would run, it could provide an srcu_struct structure for each duration. > For a (fanciful) example, you could have one srcu_struct structure for > SSDs, another for rotating rust, a third for LAN-attached storage, and > a fourth for WAN-attached storage. Maybe a fifth for lunar-based storage. All the different request_queues in a tag_set are for the same device. There might be some corner cases like storare arrays where they have different latencies. But we're not even waiting for the I/O completion here, this just protects the submission. > Does that help, or am I off in the weeds here? I think this was very helpful, and at least to be moving the srcu_struct to the tag_set sounds like a good idea to explore. Ming, anything I might have missed?