From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:47255) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Te553-0007Ty-RF for qemu-devel@nongnu.org; Thu, 29 Nov 2012 09:27:19 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Te54v-0003vA-I6 for qemu-devel@nongnu.org; Thu, 29 Nov 2012 09:27:09 -0500 Received: from mail-ee0-f45.google.com ([74.125.83.45]:63782) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Te54v-0003ul-BW for qemu-devel@nongnu.org; Thu, 29 Nov 2012 09:27:01 -0500 Received: by mail-ee0-f45.google.com with SMTP id d49so8574572eek.4 for ; Thu, 29 Nov 2012 06:27:00 -0800 (PST) Date: Thu, 29 Nov 2012 15:26:56 +0100 From: Stefan Hajnoczi Message-ID: <20121129142656.GA14196@stefanha-thinkpad.redhat.com> References: <1353597412-12232-1-git-send-email-stefanha@redhat.com> <1353597412-12232-4-git-send-email-stefanha@redhat.com> <20121129135425.GD9625@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20121129135425.GD9625@redhat.com> Subject: Re: [Qemu-devel] [PATCH v4 03/11] dataplane: add host memory mapping code List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Michael S. Tsirkin" Cc: Kevin Wolf , Anthony Liguori , qemu-devel@nongnu.org, Blue Swirl , khoa@us.ibm.com, Stefan Hajnoczi , Paolo Bonzini , Asias He On Thu, Nov 29, 2012 at 03:54:25PM +0200, Michael S. Tsirkin wrote: > On Thu, Nov 22, 2012 at 04:16:44PM +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. > > > > When the physical memory map changes the MemoryListener callbacks are > > invoked. They build up a new list of memory regions which is finally > > installed when the list has been completed. > > > > Note that this approach is not safe across memory hotplug because mapped > > pointers may still be in used across memory unplug. However, this is > > currently a problem for QEMU in general and needs to be addressed in the > > future. > > > > Signed-off-by: Stefan Hajnoczi > > Worth bothering with binary search? > vhost does a linear search over regions because > the number of ram regions is very small. memory.c does binary search. I did the same but in practice there are <20 regions for a simple VM. It's probably not worth it but without performance results this is speculation. I think there's no harm in using binary search to start with. > > +static void hostmem_listener_append_region(MemoryListener *listener, > > + MemoryRegionSection *section) > > +{ > > + Hostmem *hostmem = container_of(listener, Hostmem, listener); > > + > > + if (memory_region_is_ram(section->mr)) { > > + hostmem_append_new_region(hostmem, section); > > + } > > I think you also need to remove VGA region since you > don't mark these pages as dirty so access there won't work. I don't understand. If memory in the VGA region returns true from memory_region_is_ram(), why would there be a problem?