On 19/09/2017 08:57, Alexey Kardashevskiy wrote: >>> 3) you can consult the list (or hash table :)) of live FlatViews (which >>> means you keep it live after memory_region_transaction_commit ends, and >>> only clear it on the next call), and reuse an existing FlatView. Note >>> that the number of distinct FlatViews should be very few, >> >> I keep missing this bit - why few? Each virtio-pci device creates 2 AS, >> with proxy->modern_bar and pci_dev->bus_master_container_region which are >> unique and not aliases. Remember, 500 virtio devices is my test case ;)
Argh, no, it's me who keeps missing the bit. > More details: pci_dev->bus_master_container_region is a root and it is > enabled but its only child pci_dev->bus_master_enable_region is not. Ok, in > flatview_topology_update() I can render a FV, see that it is empty > (view->nr==0) and share an empty FV in this case too, this halves the > number of FVs (from ~1000 to ~500 for 500 virtio devices). We can also resolve "fake" aliases, obtained through a region with only one subregion. > But proxy->modern_bar (which has an modern_cfg alias which is a root of an > AS) is enabled since it is created and I could disable it and enable > afterwards but since a PCI device enablement is done by writing to the > config space, I kind of stuck here. > > I can do something like this and it helps a lot (now with -S I end up > having 4 FVs and much better start time) but it is kinda hacky and "memory: > Postpone flatview and dispatch tree building till all devices are added" > solves this better imho, no? I think modern_bar (actually modern_cfg) shouldn't have its own address space, it's a pretty wasteful way to compute the dispatch tree where a simple linked list or array would be enough: memory-region: virtio-pci 00000000fe000000-00000000fe003fff (prio 1, i/o): virtio-pci 00000000fe000000-00000000fe000fff (prio 0, i/o): virtio-pci-common 00000000fe001000-00000000fe001fff (prio 0, i/o): virtio-pci-isr 00000000fe002000-00000000fe002fff (prio 0, i/o): virtio-pci-device 00000000fe003000-00000000fe003fff (prio 0, i/o): virtio-pci-notify Paolo