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memory: avoid updating ioeventfds for some address_space

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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 by 20%.

Message-ID: <20230830032906.12488-1-hongmianquan@bytedance.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Signed-off-by: hongmianquan <hongmianquan@bytedance.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
This commit is contained in:
hongmianquan 2023-08-30 11:29:06 +08:00 committed by David Hildenbrand
parent 41ddcd2308
commit 544cff46c0
2 changed files with 13 additions and 0 deletions
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1
include/exec/memory.h
View file

@ -1095,6 +1095,7 @@ struct AddressSpace {
struct FlatView *current_map;
int ioeventfd_nb;
int ioeventfd_notifiers;
struct MemoryRegionIoeventfd *ioeventfds;
QTAILQ_HEAD(, MemoryListener) listeners;
QTAILQ_ENTRY(AddressSpace) address_spaces_link;

12
softmmu/memory.c
View file

@ -842,6 +842,10 @@ static void address_space_update_ioeventfds(AddressSpace *as)
AddrRange tmp;
unsigned i;
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 *listener, AddressSpace *as)
}
listener_add_address_space(listener, as);
if (listener->eventfd_add || listener->eventfd_del) {
as->ioeventfd_notifiers++;
}
}
void memory_listener_unregister(MemoryListener *listener)
@ -3083,6 +3091,10 @@ void memory_listener_unregister(MemoryListener *listener)
return;
}
if (listener->eventfd_add || listener->eventfd_del) {
listener->address_space->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);