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 148A1C433FE for ; Tue, 18 Oct 2022 05:20:16 +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=+HI8ygopNqUvRXTrKOyBgpqzuq5CQ/JAfCRQfZ8LgZU=; b=yINhyGzyzuGdIgu59f0O/C5n8g IqKyPLIpC0jFqzw0U4Ol8nqGpQ4V5IVASXRrP6L3O/JJYVitfwrqE0tkWTM8udNmqNblvLcwC4Y4X 9BojYoPftu0m2IWQtq+Kz8kqhAyUUZbPpNLjdkNPfbHPevxOen5dwan29dj6HDV9CxvR9qBwwoiXf cvy3CyLtwxae378w3xbGvY4ByIvR7cX+o7M1qcHIcoWVtRzGxvtRRV7r8FqBKYKqHb/7WvVG26bTO ivnQUCSWgYDkpyyB1ssCxZ667bKXzaSW6IKZEFaSEQCeH/svPH/1cTelBP9xp07H0UH/IBFnCjrJv IZMZfwgA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1okf1O-002jSZ-4U; Tue, 18 Oct 2022 05:20:10 +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 1okf1K-002jRZ-7e for linux-nvme@lists.infradead.org; Tue, 18 Oct 2022 05:20:08 +0000 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) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20221017_222006_441928_86E7776B X-CRM114-Status: GOOD ( 18.71 ) 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 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?