On 11/05/2012 10:51 AM, Jan Kiszka wrote: > On 2012-11-05 09:12, Avi Kivity wrote: > > On 11/05/2012 08:26 AM, Jan Kiszka wrote: > >> On 2012-11-04 20:21, Avi Kivity wrote: > >>> On 11/04/2012 10:30 AM, Jan Kiszka wrote: > >>>> From: Jan Kiszka <jan.kis...@siemens.com> > >>>> > >>>> Cirrus is triggering this, e.g. during Win2k boot: Changes only on > >>>> disabled regions require no topology update when transaction depth drops > >>>> to 0 again. > >>> > >>> 817dcc5368988b0 (pci: give each device its own address space) mad this > >>> much worse by multiplying the number of address spaces. Each change is > >>> now evaluated N+2 times, where N is the number of PCI devices. It also > >>> causes a corresponding expansion in memory usage. > >> > >> I know... But this regression predates your changes, is already visible > >> right after 02e2b95fb4. > >> > >>> > >>> I want to address this by caching AddressSpaceDispatch trees with the > >>> key being the contents of the FlatView for that address space. This > >>> will drop the number of distinct trees to 2-4 (3 if some devices have > >>> PCI_COMMAND_MASTER disabled, 4 if the PCI address space is different > >>> from the cpu memory address space) but will fail if we make each address > >>> space different (for example filtering out the device's own BARs). > >>> > >>> If this change also improves cpu usage sufficiently, then it will be > >>> better than your patch, which doesn't recognize changes in an enabled > >>> region inside a disabled or hidden region. > >> > >> True, though the question is how common such scenarios are. This one > >> (cirrus with win2k) is already special. > >> > >>> In other words, your patch > >>> fits the problem at hand but isn't general. On the other hand my > >>> approach doesn't eliminate render_memory_region(), just the exec.c stuff > >>> and listener updates. So we need to understand where the slowness comes > >>> from. > >> > >> I would just like to have some even intermediate solution for 1.3. We > >> can still make it more perfect later on if required. > >> > > > > I think we should apply a v2 then, the more general optimizations will > > take some time. > > OK - what should v2 do differently? >
As I noted, init and destroy cannot cause a topology update. -- I have a truly marvellous patch that fixes the bug which this signature is too narrow to contain.
