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 9181DCCF9EB for ; Wed, 29 Oct 2025 09:40:49 +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=TdX//1i3AGFErU/TEDddgO93eB4Q2X3yYIWZbw0tqrc=; b=Xd+bwZEG9u7k7AYZX7d2RrgYyi 9oWfV3B/2WAP2B8ADIBBGaZNmk3NlB2hWnVFgkcSniMGurXmOHgVUUYSAefJ3LQtAgcHj0z8OyvCI cSM5UCPqWvr6/SBS1FewvQLyP9THgwVeYy/AsTFn0wdnIFMwo4TJKvF/pOys+QViFMt3kdT1EEAGU dKlO+FL8Gq5mLAKYSgBImaC1Dx559/x+HgaeGfnYrflceT8/nTQyWjGwYrVyzRz9wPT/FzGXf2RUT 4at6m8ppodW7X4LwGQ8j9JyGMltv3/RXXEps7OCgwaKTAmINBTzS+v7oI6bkUHzlSWzO56XN4dc22 bOigyhwg==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1vE2ff-00000000XCx-3fJG; Wed, 29 Oct 2025 09:40:47 +0000 Received: from verein.lst.de ([213.95.11.211]) by bombadil.infradead.org with esmtps (Exim 4.98.2 #2 (Red Hat Linux)) id 1vE2fe-00000000XBn-00rN for linux-nvme@lists.infradead.org; Wed, 29 Oct 2025 09:40:47 +0000 Received: by verein.lst.de (Postfix, from userid 2407) id 35803227A8E; Wed, 29 Oct 2025 10:40:42 +0100 (CET) Date: Wed, 29 Oct 2025 10:40:40 +0100 From: Christoph Hellwig To: Nilay Shroff Cc: linux-nvme@lists.infradead.org, hare@suse.de, kbusch@kernel.org, hch@lst.de, sagi@grimberg.me, dwagner@suse.de, axboe@kernel.dk, gjoyce@ibm.com Subject: Re: [RFC PATCHv3 2/6] nvme-multipath: add support for adaptive I/O policy Message-ID: <20251029094040.GC1066@lst.de> References: <20251027092949.961287-1-nilay@linux.ibm.com> <20251027092949.961287-3-nilay@linux.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20251027092949.961287-3-nilay@linux.ibm.com> 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-20251029_024046_178709_BE7FA1B6 X-CRM114-Status: GOOD ( 12.36 ) 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 27, 2025 at 02:59:36PM +0530, Nilay Shroff wrote: > This commit introduces a new I/O policy named "adaptive". Users can > configure it by writing "adaptive" to "/sys/class/nvme-subsystem/nvme- > subsystemX/iopolicy" > > The adaptive policy dynamically distributes I/O based on measured > completion latency. The main idea is to calculate latency for each path, > derive a weight, and then proportionally forward I/O according to those > weights. This really sounds like a lot of overhead, and really smells of all that horrible old-school FC SAN thinking we've been carefully trying to avoid in nvme. What's the point here?