On Thu, 2011-03-31 at 14:01 -0500, Anthony Liguori wrote: > On 03/31/2011 01:49 PM, Michael S. Tsirkin wrote: > > On Thu, Mar 31, 2011 at 01:33:58PM -0500, Anthony Liguori wrote: > >> On 03/31/2011 12:43 PM, Michael S. Tsirkin wrote: > >>> Currently, vga cards that allocate vga ram, > >>> register it as regular ram. When this happens > >>> a lot, vhost need to get notified and flush > >>> its memory tables, which is slow. > >>> > >>> This was observed with cirrus vga. > >>> > >>> As a solution, add an explicit flag when > >>> registering vga ram, vhost-net can simply ignore it. > >>> > >>> Long term, we might be able to use this API > >>> to avoid the need to request > >>> dirty loggin from devices explicitly. > >>> > >>> Tested: with cirrus vga only. > >>> > >>> Signed-off-by: Michael S. Tsirkin<m...@redhat.com> > >> Treating vga specially is not the right approach. > >> > >> You want to treat real RAM specially and only make that visible to > >> vhost. See http://wiki.qemu.org/Features/RamAPI > > That seems like a dead project? And VGa is unhandled there. > > Just needs some love. > > VGA is just another device. It happens to be that we treat VGA device > memory as something that behaves like ram occassionally but that does > not make it RAM. > > Something like vhost doesn't need to see anything but RAM. If we have a > mechanism to identify RAM as RAM, then vhost can only look at RAM memory > and not worry about things like VGA. > > I thought Alex had gotten a mini-version of RamAPI in but I can't seem > to figure out what that included. At any rate, the point is still that > registering things that you want to exclude in vhost is the wrong > approach, you want to explicitly mark the things you want to include.
Conveniently I've just started to push my WIP VFIO patches out to a public tree. You can find the minimal RamAPI in these: https://github.com/awilliam/qemu-kvm-vfio/commit/182e557b544bb6e8c6cc57a2a6075d768d224082 https://github.com/awilliam/qemu-kvm-vfio/commit/a505fe08defb4fa1720fffbdf3489289bc930264 (I reserve the right to break these commits) VFIO only needs the ram_for_each_slot() interface to setup and teardown the iommu, but obviously this should include memory client type callbacks for things that only want to track memory. Alex
