From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from verein.lst.de (verein.lst.de [213.95.11.211]) (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 ADAE5264623 for ; Thu, 13 Mar 2025 09:13:54 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=213.95.11.211 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1741857237; cv=none; b=G8QIfjjS868ZMxq49lTE5Y3Z3byUmQBTynDK8WH/3bpaAVW4XUN9gp2kDFXvZe1ftHiaPY8yMoTGw9fIDG1Ql2c46QP383tIFaUrSiyPpH9HvRlDMqo36oSdYnwlyyWucP3D0o0y4tjyzQcN2H0gtimwJaIm4h1Hb13+nTH6TSw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1741857237; c=relaxed/simple; bh=D8GqWj54rNQzl6V25ALpztmfuPmNfOaft6V/tc0zXeM=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=ftveZ9WiEhap/Ixhh4RYIttNBJYnxP+bZHHTOXLEgJj6Ub5a5UlTbJTTjYJSIlTadNfde23a5Vk//qHrTAqulkwH64OTQx86sJzOCEocSY7FGh2We1eN/wPMhzTEiJI3YsJ3eqb5UR+14RCJxHVKljjFFoKpm5RxMK1vx9nltG8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=lst.de; spf=pass smtp.mailfrom=lst.de; arc=none smtp.client-ip=213.95.11.211 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=lst.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=lst.de Received: by verein.lst.de (Postfix, from userid 2407) id 3D72568AA6; Thu, 13 Mar 2025 10:13:49 +0100 (CET) Date: Thu, 13 Mar 2025 10:13:49 +0100 From: Christoph Hellwig To: Damien Le Moal Cc: Mike Christie , chaitanyak@nvidia.com, kbusch@kernel.org, hch@lst.de, 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 Subject: Re: [PATCH RFC 03/11] nvmet: Add nvmet_fabrics_ops flag to indicate SGLs not supported Message-ID: <20250313091349.GA18939@lst.de> References: <20250313052222.178524-1-michael.christie@oracle.com> <20250313052222.178524-4-michael.christie@oracle.com> <970e0d79-f338-4803-92c4-255156a8257e@kernel.org> Precedence: bulk X-Mailing-List: kvm@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: <970e0d79-f338-4803-92c4-255156a8257e@kernel.org> User-Agent: Mutt/1.5.17 (2007-11-01) 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. 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.