From mboxrd@z Thu Jan 1 00:00:00 1970 From: "J. Bruce Fields" Subject: Re: Integration of SCST in the mainstream Linux kernel Date: Mon, 4 Feb 2008 16:01:21 -0500 Message-ID: <20080204210121.GF18682@fieldses.org> References: <47A05CBD.5050803@vlnb.net> <47A7049A.9000105@vlnb.net> <1202139015.3096.5.camel@localhost.localdomain> <47A73C86.3060604@vlnb.net> <1202144767.3096.38.camel@localhost.localdomain> <47A7488B.4080000@vlnb.net> <1202145901.3096.49.camel@localhost.localdomain> <1202151989.11265.576.camel@haakon2.linux-iscsi.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org To: Linus Torvalds Cc: "Nicholas A. Bellinger" , James Bottomley , Vladislav Bolkhovitin , Bart Van Assche , Andrew Morton , FUJITA Tomonori , linux-scsi@vger.kernel.org, scst-devel@lists.sourceforge.net, Linux Kernel Mailing List , Mike Christie List-Id: linux-scsi@vger.kernel.org On Mon, Feb 04, 2008 at 11:44:31AM -0800, Linus Torvalds wrote: ... > Pure user-space solutions work, but tend to eventually be turned into > kernel-space if they are simple enough and really do have throughput and > latency considerations (eg nfsd), and aren't quite complex and crazy > enough to have a large impedance-matching problem even for basic IO stuff > (eg samba). ... > So just going by what has happened in the past, I'd assume that iSCSI > would eventually turn into "connecting/authentication in user space" with > "data transfers in kernel space". But only if it really does end up > mattering enough. We had a totally user-space NFS daemon for a long time, > and it was perfectly fine until people really started caring. I'd assumed the move was primarily because of the difficulty of getting correct semantics on a shared filesystem--if you're content with NFS-only access to your filesystem, then you can probably do everything in userspace, but once you start worrying about getting stable filehandles, consistent file locking, etc., from a real disk filesystem with local users, then you require much closer cooperation from the kernel. And I seem to recall being told that sort of thing was the motivation more than performance, but I wasn't there (and I haven't seen performance comparisons). --b.