From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Mon, 19 Aug 2013 12:09:17 +0100 From: "Richard W.M. Jones" Message-ID: <20130819110917.GD5918@redhat.com> References: <1376777374-17521-1-git-send-email-richard@nod.at> <20130819091839.GX5918@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Subject: Re: [uml-devel] [PATCH] um: ubd: Add REQ_FLUSH suppport To: Geert Uytterhoeven Cc: Richard Weinberger , Al Viro , uml-devel , "linux-kernel@vger.kernel.org" List-ID: On Mon, Aug 19, 2013 at 12:13:14PM +0200, Geert Uytterhoeven wrote: > Hi Richard, > > On Mon, Aug 19, 2013 at 11:18 AM, Richard W.M. Jones wrote: > > On Sun, Aug 18, 2013 at 12:09:34AM +0200, Richard Weinberger wrote: > >> UML's block device driver does not support write barriers, > >> to support this this patch adds REQ_FLUSH suppport. > >> Every time the block layer sends a REQ_FLUSH we fsync() now > >> our backing file to guarantee data consistency. > > > > This fixes the sync problem I saw before. So: > > What's the impact on your performance figures? It just moves the sync into the main process, thus making the "write-no-upload" test time *increase* to what we expected (the same as KVM). This doesn't address the main performance issue, which appears to lie in the serial port emulation. Rich. -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones virt-df lists disk usage of guests without needing to install any software inside the virtual machine. Supports Linux and Windows. http://people.redhat.com/~rjones/virt-df/