From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id AC0911E7C20 for ; Wed, 5 Mar 2025 23:57:48 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1741219068; cv=none; b=DSKCvhABNcDYSQPAqswLv1cbfSRqEV4gmQmTC03/P0g7aL04o+UNHs3msmZ2RHlK0g86CUpJM5hoXH2ZP76sx8X3QOeYsU/mG7kDmWF5CouWIQrBXVlZ0MVvrO6qBlpF9tjEOFcbmPnjAUBMxBw01hU+K42QzutV7cWFhmju4kQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1741219068; c=relaxed/simple; bh=sjr6OGckziQ9YjoNnbDRgjPZEbhWstKtXIcNkou+a8A=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=jkrcglvyNwz7QlBmNZnYtcvjoORsun+7ZNyOdhbAT+IZtzHsmtdmBPV4aYvx/AEmGsrzBcgd5SBAeq1QY2UhrKYVPE74jiiUPUCtyzaSsbREb7L3M+HeIZzMQeSJQmPzmvWWL9yWYdTCzjoSdpLkEpp3Kd640EASyN1XkbDX8Z4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=TkfXpqyF; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="TkfXpqyF" 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> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250305235119.GB896@lst.de> 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/