Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753478Ab1DUH2s (ORCPT ); Thu, 21 Apr 2011 03:28:48 -0400 Received: from smtp.ctxuk.citrix.com ([62.200.22.115]:36979 "EHLO SMTP.EU.CITRIX.COM" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753006Ab1DUH2r (ORCPT ); Thu, 21 Apr 2011 03:28:47 -0400 X-IronPort-AV: E=Sophos;i="4.64,250,1301875200"; d="scan'208";a="5406961" Subject: Re: [Xen-devel] Re: [PATCH v3] xen block backend. From: Ian Campbell To: Christoph Hellwig CC: Konrad Rzeszutek Wilk , "jaxboe@fusionio.com" , "xen-devel@lists.xensource.com" , "linux-kernel@vger.kernel.org" , Stefano Stabellini , "konrad@kernel.org" In-Reply-To: <20110421033735.GA11501@infradead.org> References: <1303333543-5915-1-git-send-email-konrad.wilk@oracle.com> <20110421033735.GA11501@infradead.org> Content-Type: text/plain; charset="UTF-8" Organization: Citrix Systems, Inc. Date: Thu, 21 Apr 2011 08:28:45 +0100 Message-ID: <1303370925.5997.322.camel@zakaz.uk.xensource.com> MIME-Version: 1.0 X-Mailer: Evolution 2.32.2 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1306 Lines: 29 On Thu, 2011-04-21 at 04:37 +0100, Christoph Hellwig wrote: > This should sit in userspace. And last time was discussed the issue > Stefano said the qemu Xen disk backend is just as fast as this kernel > code. And that's with an not even very optimized codebase yet. Stefano was comparing qdisk to blktap. This patch is blkback which is a completely in-kernel driver which exports raw block devices to guests, e.g. it's very useful in conjunction with LVM, iSCSI, etc. The last measurements I heard was that qdisk was around 15% down compared to blkback. By contrast blktap has a userspace component so it's not all that surprising that it turns out to be roughly equivalent to qdisk. (bear in mind that Stefano's tests were very rough and ready initial tests, not that anyone expects a more thorough benchmarking treatment to really change the result). Nobody I know of thinks blktap should go upstream since as you say there is no reason not to punt the kernel side part into userspace too. Ian. > So clear NAK for adding all this mess to the kernel. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/