From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1DYN0t-00042V-8e for qemu-devel@nongnu.org; Wed, 18 May 2005 07:46:59 -0400 Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1DYN0s-00041t-0r for qemu-devel@nongnu.org; Wed, 18 May 2005 07:46:58 -0400 Received: from [199.232.76.173] (helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1DYMwI-0003H2-7t for qemu-devel@nongnu.org; Wed, 18 May 2005 07:42:14 -0400 Received: from [131.111.8.137] (helo=ppsw-7.csi.cam.ac.uk) by monty-python.gnu.org with esmtp (Exim 4.34) id 1DYMxi-0001Ju-L7 for qemu-devel@nongnu.org; Wed, 18 May 2005 07:43:42 -0400 From: Mark Williamson Subject: Re: [Qemu-devel] Re: request : qemu-smp as target Date: Wed, 18 May 2005 12:29:38 +0100 References: <200505172121.28546.paul@codesourcery.com> <1116362494.20056.50.camel@fred.ofc.soliddesign.net> In-Reply-To: <1116362494.20056.50.camel@fred.ofc.soliddesign.net> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200505181229.38282.mark.williamson@cl.cam.ac.uk> Sender: maw48@hermes.cam.ac.uk 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: Joe Batt , Paul Brook > But how often will the virtual CPUs need the same page and is there any > other shared resource other than memory? I don't know how independent > each CPU is. Though in side discussions, everyone agrees with you, I > haven't seen numbers to convince my gut. If page only needs to be > faulted back and forth every couple million cycles, then it might work. In the applications, probably very independent. In the kernel, highly dependent: different CPUs may access shared data structures *and* protect them with spinlocks. As Paul said in a separate mail, spinlocks are going to be way more expensive in this sort of distributed environment. All that being said, a company called "Virtual Iron" has got a fully-virtualising solution that presents an SMP to the guest OS but actually distributes computation across a cluster. I have yet to see the product itself - no idea when it'll be released. It also sounds *really* difficult to make go fast but at least suggests this sort of thing can perform reasonably for some workloads. Cheers, Mark > > The only solution I can imagine being even vaguely worthwhile is a > > running user-mode qemu on top of a native openmozix system. > > OpenMosix is very interesting, but is a pain to setup. How about this: > > ssh -f host1 qemu -cpu-server $KEY > ssh -f host2 qemu -cpu-server $KEY > qemu -cpu-client host1:$KEY \ > -cpu-client host2:$KEY \ > -hda server.image > > > > I have ignorantly implemented an SH2 emulator, > > > > Cool. Any chance you're going to make these changes publicly available? > > It was a Java implementation for a customer. Not my property and not > integrated with any free software. > > > Paul