From 544cff46c018036cd66e98ffb224dd9f098065c8 Mon Sep 17 00:00:00 2001 From: hongmianquan Date: Wed, 30 Aug 2023 11:29:06 +0800 Subject: [PATCH] memory: avoid updating ioeventfds for some address_space 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 Signed-off-by: hongmianquan Signed-off-by: David Hildenbrand --- 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 cc68249eda..ef23d65afc 100644 --- a/include/exec/memory.h +++ b/include/exec/memory.h @@ -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; diff --git a/softmmu/memory.c b/softmmu/memory.c index 2cb60ec9b8..c0383a163d 100644 --- a/softmmu/memory.c +++ b/softmmu/memory.c @@ -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);