From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1Fzb9h-0001QU-Cj for qemu-devel@nongnu.org; Sun, 09 Jul 2006 11:25:09 -0400 Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1Fzb9g-0001PA-2F for qemu-devel@nongnu.org; Sun, 09 Jul 2006 11:25:08 -0400 Received: from [199.232.76.173] (helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1Fzb9f-0001P1-S4 for qemu-devel@nongnu.org; Sun, 09 Jul 2006 11:25:07 -0400 Received: from [81.29.64.88] (helo=mail.shareable.org) by monty-python.gnu.org with esmtps (TLS-1.0:DHE_RSA_AES_256_CBC_SHA:32) (Exim 4.52) id 1FzbAY-00087b-Rx for qemu-devel@nongnu.org; Sun, 09 Jul 2006 11:26:03 -0400 Date: Sun, 9 Jul 2006 16:25:04 +0100 From: Jamie Lokier Subject: Re: [Qemu-devel] add 'monitor' and 'mwait' instruction (update) Message-ID: <20060709152504.GC31080@mail.shareable.org> References: <44AD28AA.7050301@armiento.net> <1AC114B9-DB82-4F97-B0A8-831233CA2ECE@gmx.de> <44B10282.3060707@armiento.net> <200607091230.24239.paul@codesourcery.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <200607091230.24239.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: "R. Armiento" Paul Brook wrote: > qemu hardware does support DMA, but I don't think this matters. > By my reading DMA writes don't need to wake mwait. > The exact wording is "store operation", which I'd expect to mean > execution of a store instruction (by a different CPU). Hmm. x86 CPUs snoop writes by DMA as well as other CPUs, and I'd expect write snooping to be the mechanism used by 'mwait'. It would be good to test on a real system whether DMA wakes 'mwait'. I wouldn't expect many OSes to use this, but I have seen tuned networking OSes which would benefit from 'mwait' on a network DMA ring descriptor. -- Jamie