From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1IzDOw-00043h-0D for qemu-devel@nongnu.org; Mon, 03 Dec 2007 10:40:06 -0500 Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1IzDOu-00041V-DC for qemu-devel@nongnu.org; Mon, 03 Dec 2007 10:40:05 -0500 Received: from [199.232.76.173] (helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1IzDOu-00041I-6P for qemu-devel@nongnu.org; Mon, 03 Dec 2007 10:40:04 -0500 Received: from mail.codesourcery.com ([65.74.133.4]) by monty-python.gnu.org with esmtps (TLS-1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.60) (envelope-from ) id 1IzDOp-0004aT-JB for qemu-devel@nongnu.org; Mon, 03 Dec 2007 10:40:00 -0500 From: Paul Brook Subject: Re: [Qemu-devel] [PATCH 2/2 v2] Direct IDE I/O Date: Mon, 3 Dec 2007 15:39:48 +0000 References: <11966765602186@bull.net> <1196677804.5275.5.camel@frecb07144> In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200712031539.49285.paul@codesourcery.com> Reply-To: qemu-devel@nongnu.org List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: Markus Hitter On Monday 03 December 2007, Markus Hitter wrote: > Am 03.12.2007 um 11:30 schrieb Laurent Vivier: > > But if you think I should remove the buffered case, I can. > > In doubt, less code is always better. For the unlikely case you broke > something badly, there's always the option to take back the patch. > > > BTW, do you think I should enable "cache=off" by default ? > > This would be fine for a transition phase, but likely, the cache=on > case gets forgotten to be removed later. So, do it now. I think host caching is still useful enough to be enabled by default, and provides a significant performance increase in several cases. - The guest typically has a relatively small quantity of RAM, compared to a modern machine. Allowing the host OS to act as a demand-based L2 cache allows this to be used without having to dedicate excessive quantities of ram to qemu. - I've seen reports that it significantly speeds up the windows installer. - Host cache is persistent between multiple qemu runs. f you're doing anything that requires frequent guest reboots (e.g. kernel debugging) this is going to be a huge win. - You're running a host OS that has limited or no caching (e.g. DOS). I'd hope that the host OS would have cache use heuristics that would help limit cache pollution. Paul