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Re: [Qemu-devel] [PATCH v7 0/7] push mmio dispatch out of big lock

From: Jan Kiszka
Subject: Re: [Qemu-devel] [PATCH v7 0/7] push mmio dispatch out of big lock
Date: Sat, 04 May 2013 12:42:09 +0200
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On 2013-05-04 11:47, Paolo Bonzini wrote:
> Il 03/05/2013 10:04, Jan Kiszka ha scritto:
>> We can't change the semantics of opaque as long as old_mmio / old_portio
>> are around. But we need a flag anyway to indicate if a region is
>> depending on BQL or not. Adding a separate "Object *owner" to
>> MemoryRegion can serve both purposes. Then we define something like
>> void memory_region_set_local_locking(MemoryRegion *mr,
>>                                      bool local_locking,
>>                                      Object *owner);
>> to control the property (if local_locking is true, owner must be
>> non-NULL, of course). That's quite similar to my old prototype here that
>> had memory_region_set/clear_global_locking.
> I think setting the owner can be done separately from enabling local
> lock.  For example, memory_region_find could also have a variant that
> adds a ref to the owner.  It would be very similar to what Ping Fan is
> doing in the virtio-dataplane's HostMem data structure.

That's trivial to break up, but I'm not sure if there will be reasonable
scenarios where a region requires reference counting without being able
to work without the BQL. RAM, e.g., should always work BQL-free (once we
have the infrastructure in place).

And memory_region_find should likely always increment a reference if the
target region has an owner. We should convert its users to properly
dereference the region once done with it.


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