On 22/09/2017 06:45, Alexey Kardashevskiy wrote: > On 21/09/17 23:57, Paolo Bonzini wrote: >> On 21/09/2017 15:39, Alexey Kardashevskiy wrote: >>> On 21/09/17 22:07, Paolo Bonzini wrote: >>>> A container can be used instead of an alias to allow switching between >>>> multiple subregions. In this case we cannot directly share the >>>> subregions (since they only belong to a single parent), but if the >>>> subregions are aliases we can in turn walk those. >>>> >>>> While this does not reduce much the number of FlatViews that are created, >>>> it makes it possible to share the PCI bus master FlatViews and their >>>> AddressSpaceDispatch structures. For 112 virtio-net-pci devices, boot time >>>> is reduced from 25 to 10 seconds and memory consumption from 1.4 to 1 G. >>>> >>>> Signed-off-by: Paolo Bonzini <pbonz...@redhat.com> >>>> --- >>>> memory.c | 41 +++++++++++++++++++++++++++++++++++------ >>>> 1 file changed, 35 insertions(+), 6 deletions(-) >>>> >>>> diff --git a/memory.c b/memory.c >>>> index 4952cc5d84..3207ae55e2 100644 >>>> --- a/memory.c >>>> +++ b/memory.c >>>> @@ -733,12 +733,41 @@ static void render_memory_region(FlatView *view, >>>> >>>> static MemoryRegion *memory_region_get_flatview_root(MemoryRegion *mr) >>>> { >>>> - while (mr->alias && !mr->alias_offset && >>>> - int128_ge(mr->size, mr->alias->size)) { >>>> - /* The alias is included in its entirety. Use it as >>>> - * the "real" root, so that we can share more FlatViews. >>>> - */ >>>> - mr = mr->alias; >>>> + while (mr->enabled) { >>>> + if (mr->alias && !mr->alias_offset && >>>> + int128_ge(mr->size, mr->alias->size)) { >>>> + /* The alias is included in its entirety. Use it as >>>> + * the "real" root, so that we can share more FlatViews. >>>> + */ >>>> + mr = mr->alias; >>>> + continue; >>>> + } >>>> + >>>> + if (!mr->terminates) { >>> >>> Can an MR have terminates==true and children by the same time? If so, what >>> for? >> >> Yes, children override the parent. > But more important, !mr->terminates >> means that patch 3 doesn't think that MR produces an empty FlatView. > > > I see, after some debugging only MRs with @terminates==true appear in the > dispatch tree which makes sense. But I am still struggling to understand > what @terminates really means here in plain english.
As you found out, perhaps "dispatched" would be a better name than "terminates". A MR can be "alias", "terminates" or "!terminates". Aliases are resolved early. If a range is allocated to a "terminates" region A (and not to any other "terminates" region in A's subtree), it dispatches to A. If a range is allocated to a "!terminates" region B (and to any other "terminates" region in B's subtree, QEMU doesn't add it to the FlatView and it will be dispatched to another memory region: B's parent, another region in B's parent's subtree, B's grandparent, another region in B's grandparent's subtree, and so on---if nobody accepts it, it goes to unassigned_mem_ops. Paolo