Re: [Qemu-devel] [RFC PATCH qemu 3/4] memory: Share flat views and dispatch trees between address spaces

[Alexey Kardashevskiy <aik@ozlabs.ru>]

On 11/09/17 17:40, Paolo Bonzini wrote:
> On 07/09/2017 11:20, Alexey Kardashevskiy wrote:
>>  
>>      /* Accessed via RCU.  */
>>      struct FlatView *current_map;
>>  
>>      int ioeventfd_nb;
>>      struct MemoryRegionIoeventfd *ioeventfds;
>> -    struct AddressSpaceDispatch *dispatch;
>> -    struct AddressSpaceDispatch *next_dispatch;
>> +
> 
> The rough idea of the patch matches my suggestion indeed.  However, I am
> not sure why all of the changes in patch 2 are needed.

For this:

 struct MemoryRegionSection {
     MemoryRegion *mr;
-    AddressSpace *address_space;
+    AddressSpaceDispatch *dispatch;

as there are many ASes attached to the same flatview/dispatch.

And because of that, there is also:

 struct IOMMUTLBEntry {
-    AddressSpace    *target_as;
+    AddressSpaceDispatch *target_dispatch;

as the "section" in address_space_get_iotlb_entry() does not have
address_space any more, even though the only user of it -
vhost_device_iotlb_miss() - only checks if (iotlb.target_dispatch != NULL).


> Once you have built the FlatView and the dispatch within it, you can
> still cache its dispatch tree in as->dispatch, and free it with RCU from
> flatview_destroy.  This removes the need to use call_rcu from
> flatview_unref.

Ok, I will do that.

> In addition, you could change the computation of FlatView's root to
> resolve 2^64-sized aliases;

Here we reached the boundary of my english :)

Roots are given when AS/Flatview is created, and aliases are resolved already.

> also set it to NULL if the AddressSpace's
> root is disabled or the alias it resolves to is disabled (and so on
> recursively until a non-alias is found).  This should remove the need
> for address_space_root() and the change to pci_init_bus_master.




-- 
Alexey