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charset="utf-8" When updating ioeventfds, we need to iterate all address spaces, but some address spaces do not register eventfd_add|del call when memory_listener_register() and they do nothing when updating ioeventfds. So we can skip these AS in address_space_update_ioeventfds(). The overhead of memory_region_transaction_commit() can be significantly reduced. For example, a VM with 8 vhost net devices and each one has 64 vectors, can reduce the time spent on memory_region_transaction_commit b= y 20%. Signed-off-by: hongmianquan --- include/exec/memory.h | 1 + softmmu/memory.c | 12 ++++++++++++ 2 files changed, 13 insertions(+) diff --git a/include/exec/memory.h b/include/exec/memory.h index 7f5c11a0cc..556f4f1871 100644 --- a/include/exec/memory.h +++ b/include/exec/memory.h @@ -1089,6 +1089,7 @@ struct AddressSpace { struct FlatView *current_map; =20 int ioeventfd_nb; + int ioeventfd_notifiers; struct MemoryRegionIoeventfd *ioeventfds; QTAILQ_HEAD(, MemoryListener) listeners; QTAILQ_ENTRY(AddressSpace) address_spaces_link; diff --git a/softmmu/memory.c b/softmmu/memory.c index 7d9494ce70..77042d3f93 100644 --- a/softmmu/memory.c +++ b/softmmu/memory.c @@ -842,6 +842,10 @@ static void address_space_update_ioeventfds(AddressSpa= ce *as) AddrRange tmp; unsigned i; =20 + if (!as->ioeventfd_notifiers) { + return; + } + /* * It is likely that the number of ioeventfds hasn't changed much, so = use * the previous size as the starting value, with some headroom to avoid @@ -3075,6 +3079,10 @@ void memory_listener_register(MemoryListener *listen= er, AddressSpace *as) } =20 listener_add_address_space(listener, as); + + if (listener->eventfd_add || listener->eventfd_del) { + as->ioeventfd_notifiers++; + } } =20 void memory_listener_unregister(MemoryListener *listener) @@ -3083,6 +3091,10 @@ void memory_listener_unregister(MemoryListener *list= ener) return; } =20 + if (listener->eventfd_add || listener->eventfd_del) { + as->ioeventfd_notifiers--; + } + listener_del_address_space(listener, listener->address_space); QTAILQ_REMOVE(&memory_listeners, listener, link); QTAILQ_REMOVE(&listener->address_space->listeners, listener, link_as); --=20 2.11.0