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. -- I have a truly marvellous patch that fixes the bug which this signature is too narrow to contain.
