From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:55482) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1TiUEH-0008VB-SL for qemu-devel@nongnu.org; Tue, 11 Dec 2012 13:06:57 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1TiUED-0006ir-1y for qemu-devel@nongnu.org; Tue, 11 Dec 2012 13:06:53 -0500 Received: from mx1.redhat.com ([209.132.183.28]:28126) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1TiUEC-0006if-Pm for qemu-devel@nongnu.org; Tue, 11 Dec 2012 13:06:48 -0500 Date: Tue, 11 Dec 2012 20:09:56 +0200 From: "Michael S. Tsirkin" Message-ID: <20121211180956.GB9257@redhat.com> References: <1355144985-12897-1-git-send-email-stefanha@redhat.com> <1355144985-12897-4-git-send-email-stefanha@redhat.com> <20121211141340.GA18753@redhat.com> <20121211154258.GA20251@redhat.com> <87d2ygpn1f.fsf@codemonkey.ws> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87d2ygpn1f.fsf@codemonkey.ws> Subject: Re: [Qemu-devel] [PATCH v6 03/12] dataplane: add host memory mapping code List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Anthony Liguori Cc: Kevin Wolf , Stefan Hajnoczi , qemu-devel , Blue Swirl , Khoa Huynh , Stefan Hajnoczi , Paolo Bonzini , Asias He On Tue, Dec 11, 2012 at 10:32:28AM -0600, Anthony Liguori wrote: > "Michael S. Tsirkin" writes: > > > On Tue, Dec 11, 2012 at 04:27:49PM +0100, Stefan Hajnoczi wrote: > >> On Tue, Dec 11, 2012 at 3:13 PM, Michael S. Tsirkin wrote: > >> > On Mon, Dec 10, 2012 at 02:09:36PM +0100, Stefan Hajnoczi wrote: > >> >> The data plane thread needs to map guest physical addresses to host > >> >> pointers. Normally this is done with cpu_physical_memory_map() but the > >> >> function assumes the global mutex is held. The data plane thread does > >> >> not touch the global mutex and therefore needs a thread-safe memory > >> >> mapping mechanism. > >> >> > >> >> Hostmem registers a MemoryListener similar to how vhost collects and > >> >> pushes memory region information into the kernel. There is a > >> >> fine-grained lock on the regions list which is held during lookup and > >> >> when installing a new regions list. > >> > > >> > Can we export and reuse the vhost code for this? > >> > I think you will find this advantageous when you add migration > >> > support down the line. > >> > And if you find it necessary to use MemoryListener e.g. for performance > >> > reasons, then vhost will likely benefit too. > >> > >> It's technically possible and not hard to do but it prevents > >> integrating deeper with core QEMU as the memory API becomes > >> thread-safe. > >> > >> There are two ways to implement dirty logging: > >> 1. The vhost log approach which syncs dirty information periodically. > >> 2. A cheap thread-safe way to mark dirty outside the global mutex, > >> i.e. a thread-safe memory_region_set_dirty(). > > > > You don't normally want to dirty the whole region, > > you want to do this to individual pages. > > > >> If we can get thread-safe guest memory load/store in QEMU then #2 is > >> included. We can switch to using hw/virtio.c instead of > >> hw/dataplane/vring.c, we get dirty logging for free, we can drop > >> hostmem.c completely, etc. > >> > >> Stefan > > > > So why not reuse existing code? If you drop it later it won't > > matter what you used ... > > Let's not lose sight of the forest for the trees here... > > This whole series is not reusing existing code. That's really the whole > point. > > The point is to take the code (duplication and all) and then do all of > the refactoring to use common code in the tree itself. > > If we want to put this in a hw/staging/ directory, that's fine by me > too. > > Regards, > > Anthony Liguori Yes I agree. I think lack of handling for cross regin descriptors bothers me a bit more. > > > > -- > > MST