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 52C72C19F32 for ; Wed, 5 Mar 2025 23:57:55 +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=/5YN040gs3EG0en6fHi47dTm+UikR8TnkdUyJNfrloA=; b=Iedo87Ev9DqDIqbAiYVxhf+JpS zl93er8vTdg5LPeELLHnB9KTxoBX85O3/HdmMDg/CPsAVOxwD9Tnz+3Kmh63s1WpHS02TK4zwtfcO /74c/1lpkdVV+6R6W3k15Dck1Z8A36TigB8AHcl3f9d5mMl2IW/6pJ0HLMtaef9X/Rd5tyL89frau 1LbQyolyNF5/m172GaVM/z8u09JBnky+AEuU/Eh6rloC/rwkZga2IKZSfmqnDgRTtVH/0Rhv6JZEt srqyVym2WBbYqRb4kr5m5jdDvgLkBudzmhvFMGyTBY1IBhl18NKsnxdIbZ73ps1aTzFtQnnH24wxw ohOuG9+w==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98 #2 (Red Hat Linux)) id 1tpycZ-00000009egE-2B1b; Wed, 05 Mar 2025 23:57:51 +0000 Received: from nyc.source.kernel.org ([147.75.193.91]) by bombadil.infradead.org with esmtps (Exim 4.98 #2 (Red Hat Linux)) id 1tpycX-00000009efm-17ei for linux-nvme@lists.infradead.org; Wed, 05 Mar 2025 23:57:50 +0000 Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by nyc.source.kernel.org (Postfix) with ESMTP id B2E3AA467A1; Wed, 5 Mar 2025 23:52:17 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 568FFC4CEE0; Wed, 5 Mar 2025 23:57:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1741219068; bh=sjr6OGckziQ9YjoNnbDRgjPZEbhWstKtXIcNkou+a8A=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=TkfXpqyFDo5zQ9MZZ5agzkXVt7qI+0luk5+RfNUOj7cYm0Tyb3jnfo6gMD0Ut9eve ErclBYH7EOOELDoWJU0y7CoCtWIWoIta9RbmEBX6ZI1fQPzhwGcHeiazzjAu6AsBWw b5/pxh32zLr+0bJwvrrWDwtAFyZxjUdMkTOIr6awWiHiCgr+gKuMFTaAOOS/JiZJRS e7htLB10fGt1tLIFDyDQDbN+nIwMRVOV3YuYwHB4cs52aP0tLwsllPxxTIcq1xEwnp NJLejuBwEelzbGH3FpGxMNjQ8Yu58WTEdkXSsVuuY/4mcYz75kYA893hIvaW1mVvXr J+alAQyfCea2A== Date: Wed, 5 Mar 2025 16:57:44 -0700 From: Keith Busch To: Christoph Hellwig Cc: Hannes Reinecke , Sagi Grimberg , Nilay Shroff , John Meneghini , bmarzins@redhat.com, Bryan Gurney , linux-nvme@lists.infradead.org, linux-kernel@vger.kernel.org, Marco Patalano , axboe@kernel.dk Subject: Re: [PATCH] nvme: remove multipath module parameter Message-ID: References: <8a1730a1-1faf-4722-99e1-c3a85257b6f4@redhat.com> <2ff87386-c6db-4f2e-be91-213504d99a78@linux.ibm.com> <0656b66c-dd9c-495d-b1fc-4f09e763fa66@grimberg.me> <91ae613a-7b56-4ca0-b91c-6bc1eee798b8@suse.de> <20250305141554.GA18065@lst.de> <20250305235119.GB896@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250305235119.GB896@lst.de> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250305_155749_369420_36C526B1 X-CRM114-Status: GOOD ( 21.71 ) 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 Thu, Mar 06, 2025 at 12:51:19AM +0100, Christoph Hellwig wrote: > On Wed, Mar 05, 2025 at 08:17:59AM -0700, Keith Busch wrote: > > > > Plus there are some NVMe devices out there which _despite_ being PCIe do > > > > report NMIC and CMIC set (I won't name names, if you came across them > > > > you'll know) > > > > > > ????? > > > > > > NMIC and CMIC is perfectly normal and expected for multiported PCIe. > > > WTF are you talking about? > > > > Obviously he's not talking about multiported PCIe. > > Why is that obvious? No one here would think a multiported device *wouldn't* report CMIC. The fact Hannes thinks that's a questionable feature for his device gives away that it is single ported. > At least based on the stated works he talks about > PCIe and not about multi-port. The only not multiported devices I've > seen that report NMIC and CMIC are a specific firmware so that the > customer would get multipath behavior, which is a great workaround for > instable heavily switched fabrics. Note that multiported isn't always > obvious as there are quite a few hacks using lane splitting around that > a normal host can't really see. In my experience, it's left enabled because of SRIOV, which many of these devices end up shipping without supporting in PCI space anyway. > > And he's right, the > > behavior of a PCIe hot plug is very different and often undesirable when > > it's under native multipath. > > If you do actual hotplug and expect the device to go away it's indeed > not desirable. If you want the same device to come back after switched > fabric issues it is so desirable that people hack to devices to get it. > People talked about adding a queue_if_no_path-like parameter to control > keeping the multipath node alive a lot, but no one has ever invested > work into actually implementing it. Not quite the same thing, but kind of related: I proposed this device missing debounce thing about a year ago: https://lore.kernel.org/linux-nvme/Y+1aKcQgbskA2tra@kbusch-mbp.dhcp.thefacebook.com/