Re: [Qemu-devel] [RFC v1 19/22] memory: per-AddressSpace dispatch

[Blue Swirl]

On Thu, Oct 4, 2012 at 5:19 PM, Avi Kivity <address@hidden> wrote:
> On 10/04/2012 07:13 PM, Blue Swirl wrote:
>> On Thu, Oct 4, 2012 at 6:38 AM, Avi Kivity <address@hidden> wrote:
>>> On 10/03/2012 10:24 PM, Blue Swirl wrote:
>>>> >
>>>> >  #else
>>>> > -void cpu_physical_memory_rw(target_phys_addr_t addr, uint8_t *buf,
>>>> > -                            int len, int is_write)
>>>> > +
>>>> > +void address_space_rw(AddressSpace *as, target_phys_addr_t addr, 
>>>> > uint8_t *buf,
>>>> > +                      int len, bool is_write)
>>>>
>>>> I'd make address_space_* use uint64_t instead of target_phys_addr_t
>>>> for the address. It may actually be buggy for 32 bit
>>>> target_phys_addr_t  and 64 bit DMA addresses, if such architectures
>>>> exist. Maybe memory.c could be made target independent one day.
>>>
>>> We can make target_phys_addr_t 64 bit unconditionally.  The fraction of
>>> deployments where both host and guest are 32 bits is dropping, and I
>>> doubt the performance drop is noticable.
>>
>> My line of thought was that memory.c would not be tied to physical
>> addresses, but it would be more general. Then exec.c would specialize
>> the API to use target_phys_addr_t. Similarly PCI would specialize it
>> to pcibus_t, PIO to pio_addr_t and DMA to dma_addr_t.
>
> The problem is that all any transition across the boundaries would then
> involve casts (explicit or implicit) with the constant worry of whether
> we're truncating or not.  Note we have transitions in both directions,
> with the higher layer APIs calling memory APIs, and the memory API
> calling them back via MemoryRegionOps or a new MemoryRegionIOMMUOps.
>
> What does this flexibility buy us, compared to a single hw_addr fixed at
> 64 bits?

They can all be 64 bits, I'm just considering types. Getting rid of
target_phys_addr_t, pcibus_t, pio_addr_t and dma_addr_t (are there
more?) may be also worthwhile.

>
>
> --
> error compiling committee.c: too many arguments to function