From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1KzdC6-0000x0-BV for qemu-devel@nongnu.org; Mon, 10 Nov 2008 15:17:06 -0500 Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1KzdC5-0000w2-An for qemu-devel@nongnu.org; Mon, 10 Nov 2008 15:17:05 -0500 Received: from [199.232.76.173] (port=52464 helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1KzdC4-0000vu-Be for qemu-devel@nongnu.org; Mon, 10 Nov 2008 15:17:04 -0500 Received: from qw-out-1920.google.com ([74.125.92.148]:48110) by monty-python.gnu.org with esmtp (Exim 4.60) (envelope-from ) id 1KzdC4-0000G0-3r for qemu-devel@nongnu.org; Mon, 10 Nov 2008 15:17:04 -0500 Received: by qw-out-1920.google.com with SMTP id 5so1819693qwc.4 for ; Mon, 10 Nov 2008 12:17:02 -0800 (PST) Message-ID: <5d6222a80811101217q6fb85c69oe013563107420ad3@mail.gmail.com> Date: Mon, 10 Nov 2008 18:17:02 -0200 From: "Glauber Costa" Subject: Re: [Qemu-devel] [PATCH 0/4] VGA optimization In-Reply-To: <49187FC8.60107@codemonkey.ws> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Content-Disposition: inline References: <1226342253-8887-1-git-send-email-glommer@redhat.com> <49187FC8.60107@codemonkey.ws> 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 On Mon, Nov 10, 2008 at 4:39 PM, Anthony Liguori wrote: > Glauber Costa wrote: >> >> hey guys, >> > > I gave you some bad advice that I think is causing the breakage I'm seeing > now. I suggested that you simply do a lookup to find the slot given a > target_phys_addr_t but that isn't correct. Let me explain why. > > ram_addr_t represents a guest physical address. From a ram_addr_t you can > get a target_phys_addr_t. Sometimes these are the same but they aren't > always. > > You can have multiple ram_addr_t's pointing to the same target_phys_addr_t. > This is ram aliasing and it happens for a variety of reasons. In general, > it's pretty expensive to map a ram_addr_t to a target_phys_addr_t because, > among other things, for a range of (ram_addr_t, size_t), you may have many > (target_phys_addr_t, size) tuples that you have to deal with. > > vga_common_init() takes a target_phys_addr_t (well, it really takes an > unsigned long, but that's a bug). It takes this as an optimization. It > avoids having to do the conversion and ensures that it's one big linear > region. > > For dirty tracking, we have a bitmap indexed by target_phys_addr_t in QEMU. > This means that we can happily set dirty bits based on > target_phys_addr_t's. We don't have to worry about what ram_addr_t it came > from because they all map to the same bits. > > Since KVM uses a slot API, and that API is indexed in ram_addr_t's, we need > to enable dirty tracking on the ram_addr_t's. We don't have a ram_addr_t in > the VGA code. > > The solution is pretty simple. We need to keep track of the ram_addr_t's in > the VGA code and enable dirty tracking on the appropriate ram_addr_ts. > > Regards, My proposal is to let kvm interface to be: void kvm_physical_sync_dirty_bitmap(target_phys_addr_t start_addr, target_phys_addr_t end_addr, ram_addr_t phys_offset) to match, qemu then becomes: void cpu_physical_sync_dirty_bitmap(target_phys_addr_t start_addr, target_phys_addr_t end_addr, ram_addr_t phys_offset) the caller does: cpu_physical_sync_dirty_bitmap(s->map_addr, s->map_end, s->vram_offset); This way, we tell kvm which particular area of the phys_ram_bitmap to fill. I liked this interface, because then we can have the behaviour of not synchronizing back those bits into qemu, by passing NULL as the third parameter. I have a working version of it, will send shortly. > Anthony Liguori > >> I hope this is the last version (Of course, once this is merged, >> the optimizations of the optimization can start ;-) ) >> >> I split it in 4 patches. The first two ones are just moving >> things out of the way, and then #3 and #4 do the real thing. >> #3 kvm-side, #4 overall qemu. >> >> They merge most of the suggestion Anthony and Stefano's sent >> on last iteration. >> >> Hope you like it. >> >> >> >> > > > > -- Glauber Costa. "Free as in Freedom" http://glommer.net "The less confident you are, the more serious you have to act."