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Re: [PATCH v2,1/1] memory: avoid updating ioeventfds for some address_sp


From: hongmainquan
Subject: Re: [PATCH v2,1/1] memory: avoid updating ioeventfds for some address_space
Date: Mon, 4 Sep 2023 20:51:43 +0800
User-agent: Mozilla Thunderbird


Friendly ping...
Hello, this patch has already received a R-b from PeterXu. Could you please help me review it as well and see if there are any issues? If everything is fine, could you please consider merging it? Thank you!

在 2023/8/30 11:29 上午, hongmianquan 写道:
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%.

Signed-off-by: hongmianquan <hongmianquan@bytedance.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
---
v2:
-nothing has changed, just pick PeterXu's review.
---
  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;
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..178816c845 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);



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