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 3E2231EA7F4 for ; Thu, 13 Mar 2025 09:16:12 +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=1741857373; cv=none; b=cVSz05En1QmvtWNOlX3X8PQtDSbjnBsBX0DqkNnFRrq2wnfbaM/8bb3LBiB2DFG3riwQa+h1Nf6pUsxIxSO4C22ViVQV+rBA6phrW1borkr9cLF/OYZveJRAkKsLQhoetjlkI8euchsPtu24M2yw2gZCXUa4kTnirRJhRHNY8jc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1741857373; c=relaxed/simple; bh=EveOz9BzqCWNDFQacYFRdY44+wrFRTKnPnOmJi+jXac=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=JV3Y/sNMTA9qsGCPqaQufFCH57TELpBxT2cG6i6s3dOTktZvs81dMNm3wMi2Q0utP+xmfsCj3WdKjcEzSUNwy14bFkfJkvVLecunO2M9P5dpJ3OuyMYIxWqGA/6nmV2V8HiNIV+5fmCMzWpneJpcIRgFT6KZO2YDVowEiOHN/SU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=WBkj0tke; 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="WBkj0tke" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0E445C4CEDD; Thu, 13 Mar 2025 09:16:10 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1741857372; bh=EveOz9BzqCWNDFQacYFRdY44+wrFRTKnPnOmJi+jXac=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=WBkj0tkeeGRkOdQ92Bi4Fop54UxAH+yBeq7GFhdwsF7bDLgR434u8sYEt6fya67Lq 3M/FVO+peqFfKl+13tYh1n7nTUGgf1i8cOBKXlylSjBaVaJtYLRpiY5F0jBs0tenm1 wIbiI955QyNd8yADAC7Q5H9AQIbM/ddjNuiXMeLkHaF06cuVE8L7k9vampKRfTRaCh MBCXZ8KC3rndUnI62+0IrA+4x5IY7fRFHrg4fzliQb9qJN0K3vf07mX885A0MRI9Zj iUr2cArFS0Dy8HmVjJp+szltNqxCv4EXbuzSe5iQ9vjp40tQOv1abuhiATXOsLgbuH U7a2i1yuTJ2Qw== Message-ID: <574a8296-1bc5-403f-89fb-fd4cedb57c0f@kernel.org> Date: Thu, 13 Mar 2025 18:16:09 +0900 Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH RFC 03/11] nvmet: Add nvmet_fabrics_ops flag to indicate SGLs not supported To: Christoph Hellwig Cc: Mike Christie , chaitanyak@nvidia.com, kbusch@kernel.org, sagi@grimberg.me, joao.m.martins@oracle.com, linux-nvme@lists.infradead.org, kvm@vger.kernel.org, kwankhede@nvidia.com, alex.williamson@redhat.com, mlevitsk@redhat.com References: <20250313052222.178524-1-michael.christie@oracle.com> <20250313052222.178524-4-michael.christie@oracle.com> <970e0d79-f338-4803-92c4-255156a8257e@kernel.org> <20250313091349.GA18939@lst.de> Content-Language: en-US From: Damien Le Moal Organization: Western Digital Research In-Reply-To: <20250313091349.GA18939@lst.de> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 3/13/25 18:13, Christoph Hellwig wrote: > On Thu, Mar 13, 2025 at 06:02:29PM +0900, Damien Le Moal wrote: >> On 3/13/25 14:18, Mike Christie wrote: >>> The nvmet_mdev_pci driver does not initially support SGLs. In some >>> prelim testing I don't think there will be a perf gain (the virt related >>> interface may be the major bottleneck so I may not notice) so I wasn't >>> sure if they will be required/needed. This adds a nvmet_fabrics_ops flag >>> so we can tell nvmet core to tell the host we do not supports SGLS. >> >> That is a major spec violation as NVMe fabrics mandates SGL support. > > But this is a PCIe controller implementation, not fabrics. Ah ! yes ! > Fabrics does not support PRPs and has very different SGLs from the > PCIe ones. The fact that the spec conflates those in very confusing > ways is one of the big mistakes in the spec. Yes, and despite tripping on this several times with pci-epf, I did it again :) pci-epf has code for handling both PCI PRPs and SGL. We probably can make that common with mdev to facilitate SGL support. -- Damien Le Moal Western Digital Research